UNDERWRITING AGREEMENT

Exhibit 1.1

SEMGROUP ENERGY PARTNERS, L.P.

12,500,000 Common Units

Representing Limited Partner Interests

UNDERWRITING AGREEMENT

New York, New York

July 17, 2007

C ITIGROUP G LOBAL M ARKETS I NC .

M ERRILL L YNCH  & C O .

As Representatives of the several Underwriters,

c/o Citigroup Global Markets Inc.

388 Greenwich Street

New York, New York 10013

Ladies and Gentlemen:

SemGroup Holdings, L.P., a Delaware limited partnership (“ SemGroup Holdings ”), proposes to sell to the several underwriters named in Schedule I hereto (the “ Underwriters ”), for whom you (the “ Representatives ”) are acting as representatives, 12,500,000 common units (the “ Firm Units ”), each representing a limited partner interest (the “ Common Units ”) in SemGroup Energy Partners, L.P., a Delaware limited partnership (the “ Partnership ”). The Partnership also proposes to grant to the Underwriters an option to purchase up to 1,875,000 additional Common Units to cover over-allotments, if any (the “ Option Units ;” the Option Units, together with the Firm Units, being hereinafter called the “ Units ”). Certain terms used herein are defined in Section 21 hereof.

It is understood and agreed to by all parties that the Partnership was formed by subsidiaries of SemGroup, L.P., an Oklahoma limited partnership (“ SemGroup ”), to own, operate and develop a portfolio of complementary crude oil gathering, transportation, terminalling and storage assets (collectively, “ Crude Oil Assets ”) that were previously owned and operated directly or indirectly by SemGroup (the “ Crude Oil Business ”), as described more particularly in the Preliminary Prospectus (as defined herein).

It is further understood by all parties that on May 23, 2007, SemOperating G.P., L.L.C., an Oklahoma limited liability company (“ SemOperating ”), SemPipe G.P., L.L.C., a Delaware limited liability company (“ SemPipe GP ”), SemGroup, SemGroup Energy Partners, L.L.C., a Delaware limited liability company (“ New SemCrude LLC ”), and SemCrude, L.P., a Delaware limited partnership (“ SemCrude ”), entered into a Contribution, Conveyance, Assignment and Assumption Agreement (the “ Initial Contribution Agreement ”) pursuant to which:

(a) SemOperating contributed a 0.5% general partner interest in SemPipe, L.P., a Texas limited partnership (“ SemPipe ”), to SemPipe GP as a capital contribution;

(b) SemGroup contributed a 99.5% limited partner interest in SemPipe to New SemCrude LLC as a capital contribution on behalf of SemCrude; and

(c) SemCrude contributed all of the membership interests of SemPipe GP and the Crude Oil Assets to New SemCrude LLC as a capital contribution;

It is further understood and agreed to by all parties that as of the date hereof:

(a) SemGroup directly owns a 100% membership interest in SemGroup Holdings G.P., L.L.C., a Delaware limited liability company (“ Holdings GP ”);

(b) SemGroup directly owns a 99.99% limited partner interest, and Holdings GP directly owns a 0.01% general partner interest, in SemGroup Holdings;

(c) SemGroup Holdings directly owns a 100% membership interest in SemGroup Energy Partners G.P., L.L.C., a Delaware limited liability company and the sole general partner of the Partnership with a 2.0% general partner interest in the Partnership (the “ General Partner ”);

(d) the General Partner owns all of the outstanding shares of capital stock of SemGroup Energy Partners Management, Inc., a Delaware corporation (“ Employee Sub ”);

(e) SemGroup Holdings directly owns a 98.0% limited partner interest in the Partnership;

(f) The Partnership directly owns a 100% membership interest in SemGroup Energy Partners Operating, L.L.C., a Delaware limited liability company (the “ OLLC ”);

(g) SemGroup directly owns a 100% membership interest in SemOperating, and SemGroup directly owns a 99.5% limited partner interest and SemOperating directly owns a 0.5% general partner interest in SemCrude;

(h) SemCrude directly owns a 100% membership interest in New SemCrude LLC;

(i) New SemCrude LLC directly or indirectly owns all of the Crude Oil Assets; and

(j) the Partnership, as borrower, and certain subsidiaries of the Partnership, as Guarantors, entered into a $250 million Senior Secured Credit Agreement with Wachovia Bank, National Association, as administrative agent, and other lenders (together with the agreements, exhibits and attachments contemplated or included therein, “ Credit Agreement ”);

It is further understood and agreed to by all parties that the following transactions will occur on the Business Day immediately prior to the Closing Date:

(a) SemGroup, SemGroup Holdings, the General Partner, the Partnership, the OLLC and SemCrude will enter into a Closing Contribution, Conveyance, Assignment and Assumption Agreement (the “ Closing Contribution Agreement ” and, together with the Initial Contribution Agreement, the “ Contribution Agreements ”) pursuant to which:

(i) SemCrude will distribute its entire interest in New SemCrude LLC to SemGroup;

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(ii) SemGroup will contribute its 100% membership interest in New SemCrude LLC to SemGroup Holdings as a capital contribution;

(iii) SemGroup Holdings will contribute 2.0% of its membership interest in New SemCrude LLC to the General Partner as a capital contribution;

(iv) the General Partner will contribute to the Partnership its 2% membership interest in New SemCrude LLC in exchange for 511,643 general partner units representing an aggregate 2% general partner interest in the Partnership and all of the incentive distribution rights (the “ IDRs ”); and

(v) SemGroup Holdings will contribute its remaining 98.0% membership interest in New SemCrude LLC to the Partnership in exchange for 12,570,504 subordinated units, each representing a limited partner interest in the Partnership (the “ Subordinated Units ”), representing an aggregate 49.1% ownership interest in the Partnership and 12,500,000 Common Units representing an aggregate 48.9% ownership interest in the Partnership;

(b) the Partnership will contribute its interests in New SemCrude LLC to the OLLC as a capital contribution;

(c) the Partnership will borrow $137.5 million under the Credit Agreement and distribute the proceeds to SemGroup Holdings, which, in turn, will distribute the proceeds to SemGroup;

(d) SemGroup, SemManagement, L.L.C., a Delaware limited liability company and wholly-owned subsidiary of SemGroup (“ SemManagement ”), the General Partner and the Partnership will enter into an omnibus agreement (the “ Omnibus Agreement ”), which addresses the provision by SemGroup and its affiliates of personnel and general and administrative services to the Partnership and certain indemnification matters; and

(e) New SemCrude LLC and the Partnership will enter into a throughput agreement (the “ Throughput Agreement ”) with SemGroup, SemCrude and Eaglwing, L.P., a Delaware limited partnership and a wholly-owned subsidiary of SemGroup (“ Eaglwing ” and, together with SemGroup and SemCrude, the “ Customers ”), pursuant to which New SemCrude LLC provides certain gathering, transportation, terminalling and storage services to the Customers in exchange for contracted fees during an initial term that expires on December 31, 2014.

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The transactions contemplated in subsections (a) through (e) above are referred to herein as the “ Pre-Offering Transactions .”

It is further understood and agreed to by the parties hereto that the following transactions will occur on the Closing Date (as defined in Section 4):

(a) the public offering of the Firm Units contemplated hereby will be consummated;

(b) SemGroup Holdings will contribute the net proceeds of the offering of the Firm Units to SemGroup; and

(c) SemGroup will use the funds contributed to it to retire existing indebtedness.

The Pre-Offering Transactions and the transactions contemplated in subsections (a) through (c) above are collectively referred to herein as the “ Transactions .” In connection with the Transactions, the parties to the Transactions have entered or will enter into various transfer agreements, conveyances, contribution agreements and related documents (collectively, and together with the Contribution Agreements, the “ Contribution Documents ”). The Contribution Documents, the Omnibus Agreement, the Credit Agreement and the Throughput Agreement shall be collectively referred to as the “ Transaction Documents .” SemGroup, SemGroup Holdings, Holdings GP, the Partnership, the General Partner and the OLLC are hereinafter collectively referred to as the “ SemGroup Parties .” The Partnership, the General Partner, Employee Sub, the OLLC, New SemCrude LLC, SemPipe GP and SemPipe are herein collectively referred to as the “ Partnership Entities ” and, together with SemGroup, SemGroup Holdings, Holdings GP, SemCrude, SemOperating, SemManagement and Eaglwing, the “ SemGroup Entities .”

This is to confirm the agreement among the SemGroup Parties and the Underwriters concerning the purchase by the Underwriters of the Firm Units from SemGroup Holdings and of the Option Units, if any, from the Partnership.

1. Representations and Warranties . Each of the SemGroup Parties, jointly and severally, represents and warrants to, and agrees with, each Underwriter as set forth below in this Section 1.

(a) Registration . The Partnership has prepared and filed with the Commission a registration statement (file number 333-141196) on Form S-1, including a related preliminary prospectus, for registration under the Act of the offering and sale of the Units. Such Registration Statement, including all amendments thereto filed prior to the Execution Time, has become effective. The Partnership may have filed one or more amendments thereto, including a related preliminary prospectus, each of which has previously been furnished to you. The Partnership will file with the Commission a final prospectus in accordance with Rule 424(b). As filed, such final prospectus shall contain all information required by the Act and the rules thereunder and, except to the extent the Representatives shall agree in writing to a modification, shall be in all substantive respects in the form furnished to you prior to the Execution Time or, to the extent not

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completed at the Execution Time, shall contain only such specific additional information and other changes (beyond that contained in the latest Preliminary Prospectus) as the Partnership has advised you, prior to the Execution Time, will be included or made therein.

(b) No Material Misstatements or Omissions in Registration Statement or Prospectus . Each Preliminary Prospectus, at the time of filing thereof, complied in all material respects with the requirements of the Act and the rules and regulations of the Commission thereunder, and did not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. On the Effective Date, the Registration Statement did, and when the Prospectus is first filed in accordance with Rule 424(b) and on the Closing Date and on any date on which Option Units are purchased, if such date is not the Closing Date (a “ settlement date ”), the Prospectus (and any supplement thereto) will, comply in all material respects with the applicable requirements of the Act and the rules and regulations of the Commission thereunder; on the Effective Date and at the Execution Time, the Registration Statement did not and will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary in order to make the statements therein not misleading; and on the date of any filing pursuant to Rule 424(b) and on the Closing Date and any settlement date, the Prospectus (together with any supplement thereto) will not include any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; each of the statements made by the Partnership in the Registration Statement and in any Preliminary Prospectus provided to the Underwriters for use in connection with the public offering of the Units, and to be made in the Prospectus and any further amendments or supplements to the Registration Statement or Prospectus within the coverage of Rule 175(b) of the rules and regulations under the Act, including (but not limited to) any statements with respect to projected results of operations, estimated available cash and future cash distributions of the Partnership, and any statements made in support thereof or related thereto under the heading “Our Cash Distribution Policy and Restrictions on Distributions” or the anticipated ratio of taxable income to distributions, was made or will be made with a reasonable basis and in good faith; provided , however , that the Partnership makes no representations or warranties as to the information contained in or omitted from the Registration Statement, each Preliminary Prospectus or the Prospectus (or any supplement thereto) in reliance upon and in conformity with information furnished in writing to the Partnership by or on behalf of any Underwriter through the Representatives specifically for inclusion in the Registration Statement, each Preliminary Prospectus or the Prospectus (or any supplement thereto), it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 8 hereof.

(c) No Material Misstatements or Omissions in Disclosure Package . (i) The Disclosure Package and the price to the public, the number of Firm Units and the number of Option Units to be included on the cover page of the Prospectus, when taken together as a whole, and (ii) each electronic road show, when taken together as a whole with the

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Disclosure Package, and the price to the public, the number of Firm Units and the number of Option Units to be included on the cover page of the Prospectus, did not, as of the Applicable Time, contain any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from the Disclosure Package based upon and in conformity with written information furnished to the Partnership by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by or on behalf of any Underwriter consists of the information described as such in Section 8 hereof.

(d) Bona Fide Electronic Road Show . The Partnership has made available a “bona fide electronic road show” (as defined in Rule 433) such that no filing of any “road show” (as defined in Rule 433(h)) is required in connection with the offering of the Units

(e) Eligible Issuer . (i) At the time of filing the Registration Statement and (ii) as of the Execution Time (with such date being used as the determination date for purposes of this clause (ii)), the Partnership was not and is not an Ineligible Issuer (as defined in Rule 405), without taking account of any determination by the Commission pursuant to Rule 405 that it is not necessary that the Partnership be considered an Ineligible Issuer.

(f) Issuer Free Writing Prospectuses . Each Issuer Free Writing Prospectus does not include any information that conflicts with the information contained in the Registration Statement, the Preliminary Prospectus or the Prospectus. The foregoing sentence does not apply to statements in or omissions from any Issuer Free Writing Prospectus based upon and in conformity with written information furnished to the Partnership by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by or on behalf of any Underwriter consists of the information described as such in Section 8 hereof.

(g) Formation and Qualification . Each of the SemGroup Entities has been duly formed and is validly existing as a limited partnership or limited liability company, as applicable, in good standing under the laws of its jurisdiction of organization with full power and authority to enter into and perform its obligations under the Transaction Documents to which it is a party, to own or lease and to operate its properties currently owned or leased or to be owned or leased on the Closing Date and each settlement date and conduct its business as currently conducted or as to be conducted on the Closing Date and each settlement date, in each case as described in the Disclosure Package and the Prospectus. Each of the Partnership Entities is, or at the Closing Date and each settlement date will be, duly qualified to do business as a foreign limited partnership or limited liability company, as applicable and is in good standing under the laws of each jurisdiction which requires, or at the Closing Date and each settlement date will require, such qualification, except where the failure to be so qualified or registered would not have a material adverse effect on the condition (financial or otherwise), prospects, earnings, business or properties, taken as a whole, whether or not arising from transactions in the ordinary course of business, of the Partnership Entities (a “ Material Adverse Effect ”), or subject the limited partners of the Partnership to any material liability or disability.

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(h) Power and Authority to Act as a General Partner . The General Partner has, and, on the Closing Date and each settlement date, will have, full power and authority to act as general partner of the Partnership in all material respects as described in the Disclosure Package and Prospectus.

(i) Ownership of the General Partner . SemGroup Holdings owns, and on the Closing Date and each settlement date, will own, all of the issued and outstanding membership interests of the General Partner; such membership interests have been duly authorized and validly issued in accordance with the limited liability company agreement of the General Partner (as the same may be amended or restated at or prior to the Closing Date, the “ GP LLC Agreement ”), and are fully paid (to the extent required by the GP LLC Agreement) and nonassessable (except as such nonassessability may be affected by Sections 18-607 and 18-804 of the Delaware Limited Liability Company Act (the “ Delaware LLC Act ”)); and SemGroup Holdings owns such membership interests free and clear of all liens, encumbrances, security interests, charges or other claims (“ Liens ”) (except restrictions on transferability and other Liens as described in the Disclosure Package and the Prospectus).

(j) Ownership of the General Partner Interest in the Partnership . The General Partner is, and on the Closing Date and each settlement date, will be, the sole general partner of the Partnership with a 2.0% general partner interest in the Partnership; such general partner interest has been duly authorized and validly issued in accordance with the agreement of limited partnership of the Partnership (as the same may be amended or restated at or prior to the Closing Date, the “ Partnership Agreement ”); and the General Partner will own such general partner interest free and clear of all Liens (except restrictions on transferability and other Liens as described in the Disclosure Package and the Prospectus).

(k) Ownership of Subordinated Units and Incentive Distribution Rights . On the Closing Date and each settlement date, after giving effect to the Transactions, SemGroup Holdings will own 12,570,504 Subordinated Units (the “ Sponsor Units ”) and the General Partner will own 100% of the IDRs; all of such Subordinated Units and IDRs and the limited partner interests represented thereby will be duly authorized and validly issued in accordance with the Partnership Agreement, and will be fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware Limited Partnership Act (the “ Delaware LP Act ”)); and SemGroup Holdings will own the Subordinated Units and the General Partner will own the IDRs, in each case free and clear of all Liens (except restrictions on transferability and other Liens as described in the Disclosure Package and the Prospectus).

(l) Validity of the Firm Units . The Firm Units to be purchased by the Underwriters from SemGroup Holdings have been duly authorized, and, upon their issuance pursuant to the terms of the Partnership Agreement and the Closing Contribution

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Agreement, will be validly issued and fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by matters described in Section 17-607 and 17-804 of the Delaware LP Act).

(m) Validity of the Option Units . The Option Units that may be purchased by the Underwriters from the Partnership have been duly authorized for issuance and sale to the Underwriters pursuant to this Agreement and, when issued and delivered by the Partnership pursuant to this Agreement against payment of the consideration set forth herein, will be validly issued and fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by matters described in Sections 17-607 and 17-804 of the Delaware LP Act).

(n) Capitalization . At the Closing Date, after giving effect to the Transactions and the offering of the Firm Units as contemplated by this Agreement, the issued and outstanding partnership interests of the Partnership will consist of 12,500,000 Common Units, 12,570,504 Subordinated Units, 511,643 general partner units representing an aggregate 2% general partner interest in the Partnership (the “ General Partner Units ”) and the IDRs. Other than the Subordinated Units and the IDRs, the Units will be the only limited partner interests of the Partnership issued and outstanding on the Closing Date and, except for any Units issued by the Partnership in accordance with Section 5(g) of this Agreement, each settlement date.

(o) Ownership of the OLLC . On the Closing Date and each settlement date, after giving effect to the Transactions, the Partnership will own all of the issued and outstanding membership interests of the OLLC; such membership interests will be duly authorized and validly issued in accordance with the limited liability company agreement of the OLLC (as the same may be amended or restated at or prior to the Closing Date, the “ OLLC LLC Agreement ”) and will be fully paid (to the extent required by the OLLC LLC Agreement) and nonassessable (except as such nonassessability may be affected by Sections 18-607 and 18-804 of the Delaware LLC Act); and the Partnership will own such membership interests free and clear of all Liens (other than those arising under the Credit Agreement).

(p) Ownership of New SemCrude LLC . On the Closing Date and each settlement date, after giving effect to the Transactions, the OLLC will own all of the issued and outstanding membership interests of New SemCrude LLC; such membership interests will be duly authorized and validly issued in accordance with the limited liability company agreement of New SemCrude LLC (as the same may be amended or restated at or prior to the Closing Date, the “ New SemCrude LLC Agreement ”) and will be fully paid (to the extent required by the New SemCrude LLC Agreement) and nonassessable (except as such nonassessability may be affected by Sections 18-607 and 18-804 of the Delaware LLC Act); and the OLLC will own such membership interests free and clear of all Liens (other than those arising under the Credit Agreement).

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(q) Ownership of SemPipe GP . On the Closing Date and each settlement date, after giving effect to the Transactions, New SemCrude LLC will own all of the issued and outstanding membership interests of SemPipe GP; such membership interests will be duly authorized and validly issued in accordance with the limited liability company agreement of SemPipe GP (as the same may be amended or restated at or prior to the Closing Date, the “ SemPipe GP LLC Agreement ”) and will be fully paid (to the extent required by the SemPipe GP LLC Agreement) and nonassessable (except as such nonassessability may be affected by Sections 18-607 and 18-804 of the Delaware LLC Act); and New SemCrude LLC will own such membership interests free and clear of all Liens (other than those arising under the Credit Agreement).

(r) Ownership of the General Partner Interest in SemPipe . SemPipe GP is, and on the Closing Date and each settlement date, will be, the sole general partner of SemPipe with a 0.5% general partner interest in SemPipe; such general partner interest has been duly authorized and validly issued in accordance with the partnership agreement of SemPipe (as the same may be amended or restated at or prior to the Closing Date, the “ SemPipe Partnership Agreement ”); and SemPipe GP owns such general partner interest free and clear of all Liens (other than those arising under the Credit Agreement).

(s) Ownership of the Limited Partner Interest in SemPipe . On the Closing Date and each settlement date, after giving effect to the Transactions, New SemCrude LLC will own a 99.5% limited partner interest in SemPipe; such limited partner interest has been duly authorized and validly issued in accordance with the SemPipe Partnership Agreement and is fully paid (to the extent required under the SemPipe Partnership Agreement) and nonassessable (except as such nonassessability may be affected by matters described in Sections 3.03, 5.02 and 6.07 of the Texas Revised Limited Partnership Act (the “ Texas LP Act ”); and New SemCrude LLC owns such limited partner interest free and clear of all Liens (other than those arising under the Credit Agreement).

(t) Ownership of Employee Sub . On the Closing Date and each settlement date, after giving effect to the Transactions, the General Partner will own all of the outstanding shares of capital stock of Employee Sub; all of such shares have been duly authorized and validly issued and are fully paid and nonassessable; and the General Partner owns such shares free and clear of all Liens (other than those arising under the Credit Agreement).

(u) No Other Subsidiaries . Other than its ownership of its 2% general partner interest in the Partnership, the IDRs and all of the outstanding shares of capital stock of Employee Sub, the General Partner will not, on the Closing Date and each settlement date, own, directly or indirectly, any equity or long-term debt securities of any corporation, partnership, limited liability company, joint venture, association or other entity. Other than (i) the Partnership’s ownership of a 100% membership interest in the OLLC, (ii) the OLLC’s ownership of a 100% membership interest in New SemCrude LLC, (iii) New SemCrude LLC’s ownership of SemPipe GP and (iv) New SemCrude LLC’s ownership of a 99.5% limited partner interest, and SemPipe GP’s 0.5% general partner interest, in SemPipe, none of the Partnership, the OLLC, New SemCrude LLC,

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SemPipe GP or SemPipe will, on the Closing Date and each settlement date, own, directly or indirectly, any equity or long-term debt securities of any corporation, partnership, limited liability company, joint venture, association or other entity.

(v) No Preemptive Rights, Registration Rights or Options . Except as set forth in the Disclosure Package and the Prospectus, there are no (i) preemptive rights or other rights to subscribe for or to purchase, nor any restriction upon the voting or transfer of, any equity securities of the Partnership Entities or (ii) outstanding options or warrants to purchase any securities of the Partnership Entities. Neither the filing of the Registration Statement nor the offering or sale of the Units as contemplated by this Agreement gives rise to any rights for or relating to the registration of any Units or other securities of the Partnership.

(w) Authority and Authorization . Each of the SemGroup Parties has all requisite power and authority to execute and deliver this Agreement and perform its respective obligations hereunder. The Partnership has all requisite partnership power and authority to issue and deliver the Firm Units, the Sponsor Units and the IDRs to SemGroup Holdings, in accordance with and upon the terms and conditions set forth in the Partnership Agreement and the Contribution Documents. SemGroup Holdings has all requisite partnership power and authority to sell and deliver the Firm Units to the Underwriters, in accordance with and upon the terms and conditions set forth in this Agreement, the Partnership Agreement, the Disclosure Package and the Prospectus. The Partnership has all requisite partnership power and authority to issue, sell and deliver the Option Units to the Underwriters, in accordance with and upon the terms and conditions set forth in this Agreement, the Partnership Agreement, the Registration Statement, the Disclosure Package and the Prospectus. On the Closing Date and each settlement date, all partnership and limited liability company action, as the case may be, required to be taken by the SemGroup Entities or any of their respective members, stockholders or partners for the authorization, issuance, sale and delivery of the Units, the Subordinated Units, the General Partner Units and the IDRs, the execution and delivery by the SemGroup Entities of the Operative Agreements (as defined herein) and the consummation of the transactions (including the Transactions) contemplated by this Agreement and the Operative Agreements, shall have been validly taken.

(x) Authorization of this Agreement . This Agreement has been duly authorized, executed and delivered by each of the SemGroup Parties.

(y) Enforceability of Operative Agreements . At or before the Closing Date:

(i) the Partnership Agreement will have been duly authorized, executed and delivered by the General Partner and SemGroup Holdings and will be a valid and legally binding agreement of the General Partner and SemGroup Holdings, enforceable against the General Partner and SemGroup Holdings in accordance with its terms;

(ii) the GP LLC Agreement will have been duly authorized, executed and delivered by SemGroup Holdings and will be a valid and legally binding agreement of SemGroup Holdings, enforceable against SemGroup Holdings in accordance with its terms;

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(iii) the OLLC LLC Agreement has been duly authorized, executed and delivered by the Partnership and is a valid and legally binding agreement of the Partnership, enforceable against the Partnership in accordance with its terms;

(iv) the New SemCrude LLC Agreement will have been duly authorized, executed and delivered by the OLLC and will be a valid and legally binding agreement of the OLLC, enforceable against the OLLC in accordance with its terms;

(v) the SemPipe GP LLC Agreement will have been duly authorized, executed and delivered by New SemCrude LLC and will be a valid and legally binding agreement of New SemCrude LLC, enforceable against New SemCrude LLC in accordance with its terms;

(vi) the SemPipe Partnership Agreement will have been duly authorized, executed and delivered by SemPipe GP and New SemCrude LLC and will be a valid and legally binding agreement of SemPipe GP and New SemCrude LLC, enforceable against SemPipe GP and New SemCrude LLC in accordance with its terms;

(vii) the Omnibus Agreement will have been duly authorized, executed and delivered by each of the SemGroup Entities party thereto and SemManagement and will be a valid and legally binding agreement of each of the SemGroup Entities party thereto and SemManagement, enforceable against each of them in accordance with its terms;

(viii) the Credit Agreement will have been duly authorized, executed and delivered by the Partnership Entities party thereto and will be a valid and legally binding agreement of the OLLC, enforceable against the Partnership Entities party thereto, in accordance with its terms;

(ix) the Throughput Agreement will have been duly authorized, executed and delivered by the Partnership, New SemCrude LLC, SemGroup, SemCrude and Eaglwing and will be a valid and legally binding agreement of the Partnership, New SemCrude LLC, SemGroup, SemCrude and Eaglwing enforceable against the Partnership, New SemCrude LLC, SemGroup, SemCrude and Eaglwing in accordance with its terms; and

(x) the Contribution Documents will have been duly authorized, executed and delivered by the SemGroup Entities party thereto and will be valid and legally binding agreements of the SemGroup Entities party thereto, enforceable against such SemGroup Entities party thereto in accordance with their respective terms;

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provided , that, with respect to each agreement described in this Section 1(x), the enforceability thereof may be limited by bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws relating to or affecting creditors’ rights generally and by general principles of equity (regardless of whether such enforceability is considered in a proceeding in equity or at law); provided further ; that the indemnity, contribution and exoneration provisions contained in any of such agreements may be limited by applicable laws and public policy.

The Partnership Agreement, the GP LLC Agreement, the OLLC LLC Agreement, the New SemCrude LLC Agreement, the SemPipe GP LLC Agreement, the SemPipe Partnership Agreement and the Transaction Documents are herein collectively referred to as the “ Operative Agreements .”

(z) No Conflicts . None of (i) the offering, issuance or sale by the Partnership of the Option Units, (ii) the offering or sale by SemGroup Holdings of the Firm Units, (iii) the execution, delivery and performance of this Agreement and the Operative Agreements by the SemGroup Entities that are parties hereto or thereto, as the case may be, or (iv) the consummation of the Transactions and any other transactions contemplated by this Agreement or the Operative Agreements, (A) conflicts or will conflict with or constitutes or will constitute a violation of the partnership agreement, limited liability company agreement, certificate of limited partnership, certificate of formation or other constituent document (collectively, the “ Organizational Documents ”) of any of the SemGroup Entities, (B) conflicts or will conflict with or constitutes or will constitute a breach or violation of, or a default (or an event that, with notice or lapse of time or both, would constitute such a default) under any indenture, mortgage, deed of trust, loan agreement, lease or other agreement or instrument to which any of the SemGroup Entities is a party or by which any of them or any of their respective properties may be bound, (C) violates or will violate any statute, law or regulation or any order, judgment, decree or injunction of any court or governmental agency or body directed to any of the SemGroup Entities or any of their properties in a proceeding to which any of them or their property is a party or (D) results or will result in the creation or imposition of any Lien upon any property or assets of any of the Partnership Entities (other than Liens created pursuant to the Credit Agreement), which conflicts, breaches, violations, defaults or liens, in the case of clauses (B), (C) or (D), would, individually or in the aggregate, have a Material Adverse Effect or materially impair the ability of the SemGroup Entities to consummate the Transactions or any other transactions provided for in this Agreement or the Operative Agreements.

(aa) No Consents . No permit, consent, approval, authorization, order, registration, filing or qualification of or with any court, governmental agency or body having jurisdiction over any of the SemGroup Entities or any of their properties or assets is required in connection with the offering and sale of the Firm Units by SemGroup Holdings, the offering, issuance or sale by the Partnership of the Option Units, the execution, delivery and performance of this Agreement by the SemGroup Parties, the execution, delivery and performance by the SemGroup Entities that are parties thereto of their respective obligations under the Operative Agreements or the consummation of the Transactions or any other transactions contemplated by this Agreement or the Operative

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Agreements except (i) for such permits, consents, approvals and similar authorizations required under the Act, the Exchange Act and blue sky laws of any jurisdiction, (ii) for such consents that have been, or prior to the Closing Date will be, obtained, (iii) for such consents and approvals that, if not obtained, would not, individually or in the aggregate, reasonably be expected to have a Material Adverse Effect, and (iv) as disclosed in the Disclosure Package and the Prospectus.

(bb) No Defaults . None of the SemGroup Entities is in (i) violation of its Organizational Documents, (ii) violation of any statute, law, rule or regulation, or any judgment, order, injunction or decree of any court, governmental agency or body or arbitrator having jurisdiction over any of the SemGroup Entities or any of their properties or assets or (iii) breach, default (or an event which, with notice or lapse of time or both, would constitute such an event) or violation in the performance of any obligation, agreement or condition contained in any indenture, mortgage, deed of trust, loan agreement, lease or other agreement or instrument relating to the Crude Oil Business to which it is a party or by which it or any of its properties may be bound, which in the case of either (ii) or (iii) would, if continued, have a Material Adverse Effect.

(cc) Conformity of Units to Description . The Units, when issued and delivered in accordance with the terms of the Partnership Agreement and this Agreement against payment therefor as provided therein and herein, will conform in all material respects to the description thereof contained in the Disclosure Package and the Prospectus.

(dd) No Labor Dispute . Except as set forth in or contemplated in the Disclosure Package and the Prospectus, no labor problem or dispute with the SemGroup Entities’ employees who are engaged in the Crude Oil Business exists or is threatened or imminent, that could have a Material Adverse Effect.

(ee) Sufficiency of the Transaction Documents . The Transaction Documents will be legally sufficient to transfer or convey to the Partnership and its subsidiaries satisfactory title to, or valid rights to use or manage all properties not already held by it that are, individually or in the aggregate, required to enable the Partnership and its subsidiaries to conduct their operations in all material respects as contemplated by the Disclosure Package and the Prospectus, subject to the conditions, reservations, encumbrances and limitations described therein or contained in the Transaction Documents. The Partnership and it subsidiaries, upon execution and delivery of the Transaction Documents, will succeed in all material respects to the business, assets, properties, liabilities and operations reflected by the pro forma financial statements of the Partnership.

(ff) Financial Statements . The consolidated historical financial statements and schedules of the predecessor to the Partnership and its consolidated subsidiaries included in the Registration Statement, the Preliminary Prospectus and the Prospectus present fairly the financial condition, results of operations and cash flows of the predecessor to the Partnership as of the dates and for the periods indicated, comply as to form with the applicable accounting requirements of the Act and have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the

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periods involved (except as otherwise noted therein). The pro forma financial statements of the Partnership and its consolidated subsidiaries included in the Registration Statement, the Preliminary Prospectus and the Prospectus include assumptions that provide a reasonable basis for presenting the significant effects directly attributable to the transactions and events described therein, the related pro forma adjustments give appropriate effect to those assumptions, and the pro forma adjustments reflect the proper application of those adjustments to the historical financial statement amounts in the pro forma financial statements included in the Registration Statement, the Preliminary Prospectus and the Prospectus. The pro forma financial statements included in the Registration Statement, the Preliminary Prospectus and the Prospectus comply as to form in all material respects with the applicable accounting requirements of Regulation S-X under the Act and the pro forma adjustments have been properly applied to the historical amounts in the compilation of those statements. The summary historical and pro forma financial and operating information set forth in the Registration Statement, the Preliminary Prospectus and the Prospectus under the caption “Summary—Summary Historical and Unaudited Pro Forma Financial and Operating Data” and the selected historical and pro forma financial and operating information set forth under the caption “Selected Historical and Unaudited Pro Forma Financial and Operating Data” in the Registration Statement, the Preliminary Prospectus and the Prospectus is fairly presented in all material respects and prepared on a basis consistent with the audited and unaudited historical financial statements and pro forma financial statements, as applicable, from which it has been derived, unless expressly noted otherwise.

(gg) Independent Public Accountants . PricewaterhouseCoopers LLP, who has certified certain financial statements of the predecessor to the Partnership and its consolidated subsidiaries, the Partnership and its consolidated subsidiaries and the General Partner and delivered their report with respect to the audited consolidated financial statements and schedules included in the Disclosure Package and the Prospectus, is an independent registered public accounting firm with respect to the Partnership within the meaning of the Act and the applicable published rules and regulations thereunder.

(hh) No Legal Proceedings . Except as described in the Disclosure Package and the Prospectus, there is (i) no action, suit or proceeding before or by any court, arbitrator or governmental agency, body or official, domestic or foreign, now pending or, to the knowledge of any of the SemGroup Parties, threatened, to which any of the Partnership Entities is or may be a party or to which the business or property of any of the Partnership Entities is or may be subject, (ii) no statute, rule, regulation or order that has been enacted, adopted or issued by any governmental agency and (iii) no injunction, restraining order or order of any nature issued by a federal or state court or foreign court of competent jurisdiction to which any of the Partnership Entities is or may be subject, that, in the case of clauses (i), (ii) and (iii) above, is reasonably expected to (A) individually or in the aggregate have a Material Adverse Effect, (B) prevent or result in the suspension of the offering and issuance of the Units, or (C) draw into question the validity of this Agreement.

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(ii) Title to Properties . Following consummation of the Transactions and on the Closing Date and each settlement date, the Partnership Entities will have good and marketable title to all real property and good title to all personal property described in the Disclosure Package or the Prospectus as owned by the Partnership Entities, free and clear of all Liens except (i) as described, and subject to limitations contained, in the Disclosure Package and the Prospectus, (ii) that arise under the Credit Agreement or (iii) such as do not materially interfere with the use of such properties taken as a whole as they have been used in the past and are proposed to be used in the future as described in the Disclosure Package and the Prospectus; provided , that, with respect to any real property and buildings held under lease by the Partnership Entities, such real property and buildings are held under valid and subsisting and enforceable leases with such exceptions as do not materially interfere with the use of the properties of the Partnership Entities taken as a whole as they have been used in the past as described in the Disclosure Package and the Prospectus and are proposed to be used in the future as described in the Disclosure Package and the Prospectus.

(jj) Rights-of-Way . Following consummation of the Transactions and on the Closing Date and each settlement date, the Partnership Entities will have such easements or rights-of-way from each person (collectively, “ rights-of-way ”) as are necessary to conduct their business in the manner described, and subject to the limitations contained, in the Disclosure Package and the Prospectus, except for (i) qualifications, reservations and encumbrances that would not have, individually or in the aggregate, a Material Adverse Effect and (ii) such rights-of-way that, if not obtained, would not have, individually or in the aggregate, a Material Adverse Effect; other than as set forth, and subject to the limitations contained, in the Disclosure Package and the Prospectus, the Partnership Entities have, or following consummation of the Transactions will have, fulfilled and performed all their material obligations with respect to such rights-of-way and no event has occurred that allows, or after notice or lapse of time would allow, revocation or termination thereof or would result in any impairment of the rights of the holder of any such rights-of-way, except for such revocations, terminations and impairments that would not have a Material Adverse Effect; and, except as described in the Disclosure Package and the Prospectus, none of such rights-of-way contains any restriction that is materially burdensome to the Partnership Entities, taken as a whole.

(kk) Transfer Taxes . There are no transfer taxes or other similar fees or charges under federal law or the laws of any state, or any political subdivision thereof, required to be paid in connection with the execution and delivery of this Agreement or the issuance by the Partnership of the Units, the sale by SemGroup Holdings of the Firm Units or the sale by the Partnership of the Option Units.

(ll) Tax Returns . Each of the Partnership Entities has filed all foreign, federal, state and local tax returns that are required to be filed or has requested extensions thereof, except in any case in which the failure so to file would not have a Material Adverse Effect and has paid all taxes required to be paid by it and any other assessment, fine or penalty levied against it, to the extent that any of the foregoing is due and payable, except for any such assessment, fine or penalty that is currently being contested in good faith or as would not have a Material Adverse Effect.

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(mm) Insurance . The SemGroup Entities carry or are entitled to the benefits of, and following the consummation of the Transactions and on the Closing Date and each settlement date the Partnership Entities will carry or be entitled to the benefits of, insurance relating to the Crude Oil Assets, with financially sound and reputable insurers, in such amounts and covering such risks as is commercially reasonable, and all such insurance is in full force and effect. The SemGroup Parties have no reason to believe that the Partnership Entities will not be able (i) to renew their existing insurance coverage relating to the Crude Oil Assets as and when such policies expire or (ii) to obtain comparable coverage relating to the Crude Oil Assets from similar institutions as may be necessary or appropriate to conduct such business as now conducted and at a cost that would not reasonably be expected to have a Material Adverse Effect.

(nn) Distribution Restrictions . No subsidiary of the Partnership is currently prohibited, directly or indirectly, from paying any distributions to the Partnership, from making any other distribution on such subsidiary’s equity interests, from repaying to the Partnership any loans or advances to such subsidiary from the Partnership or from transferring any of such subsidiary’s property or assets to the Partnership or any other subsidiary of the Partnership, except as described in or contemplated by the Disclosure Package and the Prospectus or arising under the Credit Agreement.

(oo) Possession of Licenses and Permits . The SemGroup Entities possess such permits, licenses, approvals, consents and other authorizations (collectively, “ Governmental Licenses ”) issued by the appropriate federal, state, local or foreign regulatory agencies or bodies necessary to conduct the Crude Oil Business, except where the failure so to possess would not, singly or in the aggregate, result in a Material Adverse Effect; the SemGroup Entities are in compliance with the terms and conditions of all such Governmental Licenses, except where the failure so to comply would not, singly or in the aggregate, result in a Material Adverse Effect; all of the Governmental Licenses are valid and in full force and effect, except when the invalidity of such Governmental Licenses or the failure of such Governmental Licenses to be in full force and effect would not, singly or in the aggregate, result in a Material Adverse Effect; and the SemGroup Entities have not received any notice of proceedings relating to the revocation or modification of any such Governmental Licenses which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, would result in a Material Adverse Effect.

(pp) Environmental Laws . With respect to the Crude Oil Assets, each of the SemGroup Entities (i) is in compliance with applicable federal, state and local laws and regulations relating to the prevention of pollution or protection of the environment or imposing liability or standards of conduct concerning any Hazardous Materials (as defined below) (“ Environmental Laws ”), (ii) has received all permits required of them under applicable Environmental Laws to conduct their respective businesses as presently conducted or as proposed to be conducted in the future as described in the Disclosure Package and the Prospectus, (iii) is in compliance with all terms and conditions of any such permits and (iv) does not have any liability in connection with the release into the environment of any Hazardous Material, except where such noncompliance with Environmental Laws, failure to receive required permits, failure to comply with the terms

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and conditions of such permits or liability in connection with such releases would not, individually or in the aggregate, have a Material Adverse Effect. The term “ Hazardous Material ” means (A) any “hazardous substance” as defined in the Comprehensive Environmental Response, Compensation and Liability Act of 1980, as amended, (B) any “hazardous waste” as defined in the Resource Conservation and Recovery Act, as amended, (C) any petroleum or petroleum product, (D) any polychlorinated biphenyl and (E) any pollutant or contaminant or hazardous, dangerous or toxic chemical, material, waste or substance regulated under or within the meaning of any applicable Environmental Law. In the ordinary course of business, the SemGroup Entities periodically review the effect of Environmental Laws on their business, operations and properties, in the course of which they identify and evaluate costs and liabilities that are reasonably likely to be incurred pursuant to such Environmental Laws (including, without limitation, any capital or operating expenditures required for clean-up, closure of properties or compliance with Environmental Laws, or any permit, license or approval, any related constraints on operating activities and any potential liabilities to third parties). On the basis of such review, the SemGroup Entities have reasonably concluded that such associated costs and liabilities relating to the Crude Oil Business would not, singly or in the aggregate, have a Material Adverse Effect.

(qq) Possession of Intellectual Property . Except for such exceptions that would not reasonably be expected to result in a Material Adverse Effect, (i) the SemGroup Entities own or possess, or can acquire or use on reasonable terms, adequate patents, patent rights, licenses, inventions, copyrights, know how (including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems or procedures), trademarks, service marks, trade names or other intellectual property necessary to carry on the Crude Oil Business (collectively, “ Intellectual Property ”), and (ii) the SemGroup Entities have not received any notice and are not otherwise aware of any infringement of or conflict with asserted rights of others with respect to any Intellectual Property or of any facts or circumstances that would render any Intellectual Property invalid or inadequate to protect the interest of the SemGroup Entities.

(rr) Certain Relationships and Related Transactions . No relationship, direct or indirect, exists between or among any Partnership Entity, on the one hand, and the directors, officers, stockholders, affiliates, customers or suppliers of any Partnership Entity, on the other hand, that is required to be described in the Preliminary Prospectus or the Prospectus and is not so described.

(ss) ERISA . On the Closing Date and each settlement date, each Partnership Entity will be in compliance in all material respects with all presently applicable provisions of the Employee Retirement Income Security Act of 1974, as amended, including the regulations and published interpretations thereunder (“ ERISA ”); no “reportable event” (as defined in ERISA) has occurred with respect to any “pension plan” (as defined in ERISA) for which any Partnership Entity (after giving effect to the Transactions) would have any liability, excluding any reportable event for which a waiver could apply; no Partnership Entity (after giving effect to the Transactions) expects to incur liability under (i) Title IV of ERISA with respect to termination of, or withdrawal from, any “pension plan” or (ii) Sections 412 or 4971 of the Internal Revenue Code of 1986, as amended, including the regulations and published interpretations thereunder (the “ Code ” ). None of the Partnership Entities maintain a “pension plan.”

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(tt) Description of Legal Proceedings and Contracts; Filing of Exhibits . There are no legal or governmental proceedings pending or, to the knowledge of the SemGroup Parties, threatened or contemplated, against any of the SemGroup Entities, or to which any of the SemGroup Entities is a party, or to which any of their properties or assets, or to which the Crude Oil Business, is subject, that are required to be described in the Registration Statement or the Disclosure Package that are not described as required, and there are no agreements, contracts, indentures, leases or other instruments that are required to be described in the Registration Statement or the Disclosure Package or to be filed as an exhibit to the Registration Statement that are not described or filed as required by the Act or the Exchange Act or the rules and regulations thereunder. The statements included in the Registration Statement and the Disclosure Package, insofar as such statements summarize legal matters, agreements, documents or proceedings discussed therein, are accurate summaries of such legal matters, agreements, documents or proceedings.

(uu) Sarbanes-Oxley Act of 2002 . On and after the Closing Date, the Partnership will be in compliance in all material respects with all applicable provisions of the Sarbanes-Oxley Act of 2002, the rules and regulations promulgated in connection therewith and the rules of the Nasdaq Global Market (the “ Nasdaq ”) that are effective and applicable to the Partnership.

(vv) Investment Company . None of the Partnership Entities is nor, after giving effect to the Transactions and the offering and sale of the Option Units and the application of the proceeds thereof as described in the Disclosure Package and the Prospectus, will any of the Partnership Entities be an “investment company” or a company “controlled by” an “investment company,” each as defined in the Investment Company Act of 1940, as amended (the “ Investment Company Act ”).

(ww) Internal Accounting Controls . Each Partnership Entity maintains a system of internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences. Each Partnership Entity’s internal controls over financial reporting are effective and none of the Partnership Entities is aware of any material weakness in their internal control over financial reporting.

(xx) Disclosure Controls and Procedures . (i) Each Partnership Entity has established and maintains disclosure controls and procedures (to the extent required by and as such term is defined in Rule 13a-15 under the Exchange Act), (ii) such disclosure controls and procedures are designed to ensure that the information required to be

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disclosed by the Partnership in the reports it files or will file or submit under the Exchange Act, as applicable, is accumulated and communicated to management of the General Partner, including their respective principal executive officers and principal financial officers, as appropriate, to allow timely decisions regarding required disclosure to be made and (iii) such disclosure controls and procedures are effective in all material respects to perform the functions for which they were established to the extent required by Rule 13a-15 of the Exchange Act.

(yy) Market Stabilization . None of the SemGroup Entities has taken, directly or indirectly, any action designed to or that would constitute or that might reasonably be expected to cause or result in, under the Exchange Act or otherwise, stabilization or manipulation of the price of any security of the Partnership to facilitate the sale or resale of the Units.

(zz) No Loans to Directors and Officers . The Partnership Entities have not extended credit in the form of a personal loan made, directly or indirectly, by any of the Partnership Entities to any director or executive officer of any of the Partnership Entities or to any family member or affiliate of any director or executive officer of any of the Partnership Entities.

(aaa) Foreign Corrupt Practices Act. No SemGroup Entity nor, to the knowledge of the SemGroup Parties, any director, officer, agent, employee or affiliate of any Partnership Entity is aware of or has taken any action, directly or indirectly, that would result in a violation by such Persons of the Foreign Corrupt Practices Act of 1977, as amended, and the rules and regulations thereunder (collectively, the “ FCPA ”), including, without limitation, making use of the mails or any means or instrumentality of interstate commerce corruptly in furtherance of an offer, payment, promise to pay or authorization of the payment of any money, or other property, gift, promise to give, or authorization of the giving of anything of value to any “foreign official” (as such term is defined in the FCPA) or any foreign political party or official thereof or any candidate for foreign political office, in contravention of the FCPA, and the SemGroup Entities and, to the knowledge of the SemGroup Parties, their affiliates have conducted their businesses in compliance with the FCPA and have instituted and maintain policies and procedures designed to ensure, and which are reasonably expected to continue to ensure, continued compliance therewith.

(bbb) Money Laundering Laws . The operations of the SemGroup Entities are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, the money laundering statutes of all jurisdictions, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “ Money Laundering Laws ”) and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving any of the SemGroup Entities with respect to the Money Laundering Laws is pending or, to the best knowledge of the SemGroup Parties, threatened.

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(ccc) Office of Foreign Assets Control . No SemGroup Entity nor, to the knowledge of the SemGroup Parties, any director, officer, agent, employee or affiliate of any SemGroup Entity is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Treasury Department (“ OFAC ”); and the Partnership will not directly or indirectly use the proceeds of the offering, or lend, contribute or otherwise make available such proceeds to any subsidiary, joint venture partner or other person or entity, for the purpose of financing the activities of any person currently subject to any U.S. sanctions administered by OFAC.

(ddd) Lending Relationship . Except as disclosed in the Disclosure Package and the Prospectus, no SemGroup Entity (i) has any material lending or other relationship with any bank or lending affiliate of any of the Underwriters and (ii) intends to use any of the proceeds from the sale of the Units hereunder to repay any outstanding debt owed to any affiliate of the Underwriters.

(eee) Private Placement . The issuance and sale of 12,500,000 Common Units and 12,570,504 Subordinated Units to SemGroup Holdings and the issuance and sale of the General Partner Units and the IDRs to the General Partner is exempt from the registration requirements of the Act, the rules and regulations and the securities laws of any state having jurisdiction with respect thereto, and none of the SemGroup Entities has taken or will take any action that would cause the loss of such exemption.

(fff) Statistical Data . Any statistical and market-related data included in the Disclosure Package or the Prospectus are based on or derived from sources that the Partnership believes to be reliable and accurate, and the Partnership has obtained the written consent to the use of such data from such sources to the extent required.

(ggg) No Distribution of Other Offering Materials . None of the SemGroup Entities has distributed and, prior to the later to occur of the Closing Date or any settlement date and completion of the distribution of the Units, will distribute any offering material in connection with the offering and sale of the Units other than any Preliminary Prospectus, the Prospectus, any Issuer Free Writing Prospectus to which the Representative has consented in accordance with this Agreement, any other materials, if any, permitted by the Act, including Rule 134.

(hhh) Listing on the Nasdaq . The Units have been approved to be listed on the Nasdaq, subject to official notice of issuance.

Any certificate signed by any officer of any of the SemGroup Parties and delivered to the Representatives or counsel for the Underwriters in connection with the offering of the Units shall be deemed a representation and warranty by such entity, as to matters covered thereby, to each Underwriter.

2. Additional Representations and Warranties by SemGroup, SemGroup Holdings and Holdings GP . SemGroup, SemGroup Holdings and Holdings GP also represent and warrant to each Underwriter as set forth below in this Section 2.

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(a) Valid Title . At the Closing Date and after giving effect to the Pre-Offering Transactions, SemGroup Holdings will have valid title to the Firm Units, free and clear of all Liens, and will have the legal right and power to sell, transfer and deliver the Firm Units or a valid security entitlement in respect of such Firm Units, as the case may be.

(b) Delivery of Firm Units . Upon payment of the purchase price for the Firm Units, delivery (as defined in Section 8-301 of the New York Uniform Commercial Code (the “ UCC ”) of such Firm Units, as directed by the Underwriters, to Cede & Co. (“ Cede ”) or such other nominee as may be designated by The Depository Trust Company (“ DTC ”), registration of such Firm Units in the name of Cede or such other nominee, and the crediting of such Firm Units on the books of DTC to securities accounts of the Underwriters (assuming that neither DTC nor any such Underwriter has notice of any adverse claim within the meaning of Section 8-105 of the UCC to such Firm Units), (A) DTC shall be a “protected purchaser,” within the meaning of Section 8-303 of the UCC, of such Firm Units and will acquire its interest in the Firm Units (including, without limitation, all rights that SemGroup Holdings had or has the power to transfer in such Firm Units) free and clear of any adverse claim within the meaning of Section 8-102 of the UCC, (B) under Section 8-501 of the UCC, the Underwriters will acquire a valid security entitlement in respect of such Firm Units and (C) no action (whether framed in conversion, replevin, constructive trust, equitable lien or other theory) based on any “adverse claim,” within the meaning of Section 8-102 of the UCC, to such Firm Units may be asserted against the Underwriters with respect to such security entitlement. For purposes of this representation, SemGroup Holdings may assume that when such payment, delivery and crediting occur, (1) such Firm Units will have been registered in the name of Cede or another nominee designated by DTC, in each case on the Partnership’s unit registry in accordance with its certificate of formation, agreement of limited partnership and applicable law, (2) DTC will be registered as a “clearing corporation” within the meaning of Section 8-102 of the UCC and will have established a “securities account” for the Underwriters within the meaning of Section 8-501(a) of the UCC and (3) appropriate entries to the accounts of the several Underwriters on the records of DTC will have been made pursuant to the UCC.

(c) No Association with NASD Members . None of the SemGroup Parties nor any of their affiliates directly, or indirectly through one or more intermediaries, controls, or is controlled by, or is under common control with, or is a person associated with (within the meaning of Article I(dd) of the By-laws of the NASD), any member firm of the NASD.

3. Purchase and Sale . (a) Subject to the terms and conditions and in reliance upon the representations and warranties herein set forth, SemGroup Holdings agrees to sell to each Underwriter, and each Underwriter agrees, severally and not jointly, to purchase from SemGroup Holdings, at a purchase price of $20.6525 per unit, the amount of the Firm Units set forth opposite such Underwriter’s name in Schedule I hereto.

(b) Subject to the terms and conditions and in reliance upon the representations and warranties herein set forth, the Partnership hereby grants an option to the several Underwriters to purchase, severally and not jointly, up to 1,875,000 Option Units at the same purchase price per

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unit as the Underwriters shall pay for the Firm Units. Said option may be exercised only to cover over-allotments in the sale of the Firm Units by the Underwriters. Said option may be exercised in whole or in part at any time on or before the 30th day after the date of the Prospectus upon written or telegraphic notice by the Representatives to the Partnership setting forth the number of Option Units as to which the several Underwriters are exercising the option and the settlement date. The number of Option Units to be purchased by each Underwriter shall be the same percentage of the total number of Option Units to be purchased by the several Underwriters as such Underwriter is purchasing of the Firm Units, subject to such adjustments as the Representatives in their absolute discretion shall make to eliminate any fractional Units.

4. Delivery and Payment . Delivery of and payment for the Firm Units and the Option Units (if the option provided for in Section 3(b) hereof shall have been exercised on or before the third Business Day immediately preceding the Closing Date) shall be made at 10:00 AM, New York City time, on July 23, 2007, or at such time on such later date not more than three Business Days after the foregoing date as the Representatives shall designate, which date and time may be postponed by agreement between the Representatives and the Partnership or as provided in Section 9 hereof (such date and time of delivery and payment for the Units being herein called the “ Closing Date ”). Delivery of the Units shall be made to the Representatives for the respective accounts of the several Underwriters against payment by the several Underwriters