PURCHASE AND SALE AGREEMENT

Exhibit 2.1

Execution Copy

PURCHASE AND SALE AGREEMENT

by and between

SEMCRUDE, L.P.

(“Seller”)

and

SEMGROUP ENERGY PARTNERS, L.L.C.

(“Buyer”)

May 12, 2008

TABLE OF CONTENTS

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TABLE OF CONTENTS

(continued)

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TABLE OF CONTENTS

(continued)

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PURCHASE AND SALE AGREEMENT

THIS PURCHASE AND SALE AGREEMENT, dated as of May 12, 2008 (this “ Agreement ”), is entered into by and among SemCrude, L.P., a limited partnership organized under the Laws of the State of Delaware (“ Seller ”), and SemGroup Energy Partners, L.L.C., a limited liability company organized under the Laws of the State of Delaware (“ Buyer ”).

RECITALS

WHEREAS , Seller owns a certain crude oil pipeline, pumping facilities and associated assets; and

WHEREAS , Seller desires to sell, and Buyer desires to purchase, such assets on the terms and conditions set forth in this Agreement.

NOW, THEREFORE , in consideration of the premises and mutual covenants contained herein and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Parties agree as follows:

ARTICLE I

DEFINITIONS AND RULES OF CONSTRUCTION

Section 1.1 Definitions . As used herein, the following terms shall have the following meanings:

“ Acquired Assets ” has the meaning provided such term in Section 2.1 .

“ Affiliate ” means, with respect to any Person, any other Person that, directly or indirectly, controls, is controlled by or is under common control with, such specified Person through one or more intermediaries or otherwise; provided , however , for purposes of this Agreement, MLP GP, MLP and MLP’s Subsidiaries, including Buyer, shall not be deemed to be Affiliates of Seller and Seller and its parent entities and affiliates shall not be deemed to be Affiliates of MLP GP, MLP and MLP’s Subsidiaries, including Buyer. For the purposes of this definition, “control” means, where used with respect to any Person, the possession, directly or indirectly, of the power to direct or cause the direction of the management and policies of such Person, whether through the ownership of voting securities, by contract or otherwise, and the terms “controlling” and “controlled” have correlative meanings.

“ Agreement ” has the meaning provided such term in the preamble to this Agreement.

“ Ancillary Documents ” means the Buyer Ancillary Documents and the Seller Ancillary Documents.

“ Assignment and Assumption Agreement ” means that certain Assignment and Assumption by and between Buyer and Seller substantially in the form of Exhibit A attached hereto.

“ Assignment and Assumption of Leases and Rights-of-Way ” means that certain Assignment and Assumption of Leases and Rights-of-Way by and between Buyer and Seller in the form of Exhibit B attached hereto.

“ Assumed Obligations ” has the meaning provided such term in Section 2.6 .

“ Bill of Sale ” means the Bill of Sale of Seller in the form of Exhibit C attached hereto.

“ Business Day ” means any day that is not a Saturday, Sunday or legal holiday in the State of Oklahoma or a federal holiday in the United States.

“ Buyer ” has the meaning provided such term in the preamble to this Agreement.

“ Buyer Ancillary Document ” means each agreement, document or certificate to be delivered by Buyer at Closing pursuant to Section 2.4(c) .

“ Buyer Approvals ” has the meaning provided such term in Section 5.3 .

“ Buyer Entities ” means Buyer, MLP, MLP GP and SMEP.

“ Buyer Indemnified Parties ” has the meaning provided such term in Section 8.2(a) .

“ Claim Notice ” has the meaning provided such term in Section 8.3(a) .

“ Closing ” has the meaning provided such term in Section 2.4(a) .

“ Closing Date ” has the meaning provided such term in Section 2.4(a) .

“ Code ” means the Internal Revenue Code of 1986, as amended.

“ Conflicts Committee ” means the conflicts committee of the board of directors of MLP GP.

“ Contract ” means any legally binding agreement, commitment, lease, license or contract, including any amendments, modifications and supplements thereto.

“ Deeds ” has the meaning provided such term in Section 2.4(b)(i) .

“ Disclosure Schedule ” means the schedules attached hereto.

“ Dollars ” and “ $ “ mean the lawful currency of the United States.

“ Eaglwing ” means Eaglwing, L.P., an Oklahoma limited partnership.

“ Effective Time ” has the meaning provided such term in Section 2.4(a) .

“ Environmental Law ” means any applicable Law relating to health, safety, the environment, natural resources, or the protection thereof, including any applicable provisions of the Comprehensive Environmental Response, Compensation and Liability Act, 42 U.S.C. § 9601 et seq ., the Hazardous Materials Transportation Act, 49 U.S.C. § 5101 et seq ., the Resource Conservation and Recovery Act, 42 U.S.C. § 6901 et seq ., the Clean Water Act, 33 U.S.C. § 1251 et seq ., the Clean Air Act, 42 U.S.C. § 7401 et seq ., the Toxic Substances Control Act, 15 U.S.C. § 2601 et seq ., the Federal Insecticide, Fungicide, and Rodenticide Act, 7 U.S.C. § 136 et seq ., the Oil Pollution Act of 1990, 33 U.S.C. § 2701 et seq ., the Safe Drinking Water Act, 42 U.S.C. § 300f et seq ., the Pipeline Safety Act, as amended by the Pipeline Inspection, Protection, Enforcement and Safety Act of 2006, 49 U.S.C. § 60101 et seq ., and any other applicable Law relating to health, safety, the environment, natural resources or the protection thereof, and all analogous state or local statutes, and the regulations promulgated pursuant thereto.

“ Excess Expenses ” has the meaning provided such term in Section 6.6 .

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“ Excluded Assets ” has the meaning provided such term in Section 2.5 .

“ Fundamental Representations and Warranties ” means the representations and warranties contained in Sections 3.1 , 3.2 , 4.1 and 4.6(a) .

“ GAAP ” means generally accepted accounting principles of the United States, consistently applied.

“ Governmental Authority ” means any federal, state, municipal, local or similar governmental authority, regulatory or administrative agency, court or arbitral body.

“ Hazardous Substance(s) ” means and includes, each substance defined, designated, classified or regulated as a hazardous waste, hazardous substance, hazardous material, pollutant, contaminant, radioactive material or byproduct, or toxic substance under any Environmental Law and any petroleum or petroleum products.

“ Indebtedness ” means with respect to any Person, at any date, without duplication, (a) all obligations of such Person for borrowed money, including all principal, interest, premiums, fees, expenses, overdrafts and penalties with respect thereto, (b) all obligations of such Person evidenced by bonds, debentures, notes or other similar instruments, (c) all obligations of such Person to pay the deferred purchase price of property, except trade payables incurred in the ordinary course of business, (d) all obligations of such Person to reimburse any bank or other Person in respect of amounts paid under a letter of credit or similar instrument, (e) all capitalized lease obligations, (f) all other obligations of a Person which would be required to be shown as indebtedness on a balance sheet of such Person prepared in accordance with GAAP, and (g) all indebtedness of any other Person of the type referred to in clauses (a) to (f) above directly or indirectly guaranteed by such Person or secured by any assets of such Person, whether or not such indebtedness has been assumed by such Person.

“ Indemnified Party ” has the meaning provided such term in Section 8.3(a) .

“ Indemnifying Party ” has the meaning provided such term in Section 8.3(a) .

“ Knowledge ” as to Buyer means the actual knowledge, after due inquiry, of those Persons listed in Schedule 1.1(i) and as to Seller means the actual knowledge, after due inquiry, of those Persons listed in Schedule 1.1(ii) .

“ Land ” has the meaning provided such term in Section 2.1(b) .

“ Law ” means any applicable law (including common law) rule, regulation, ordinance, order, judgment or decree of a Governmental Authority, in each case as in effect on and as interpreted on the date of this Agreement.

“ Leases ” has the meaning provided such term in Section 2.1 (c) .

“ Lien(s) ” means, with respect to any property or asset, any mortgage, pledge, charge, security interest or other encumbrance of any kind in respect of such property or asset.

“ Losses ” means all actual liabilities, losses, damages, fines, penalties, judgments, settlements, awards, costs and expenses (including reasonable fees and expenses of counsel); provided, however , the foregoing definition of “Losses” is subject to and restricted by the provisions of Section 8.7(b) .

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“ Material Adverse Effect ” means any circumstance, change or effect that (a) is materially adverse to the business, operations or financial condition of a Person or the operation of the Acquired Assets (b) that materially impedes the ability of a Person to complete the transactions contemplated herein, but shall exclude any circumstance, change or effect resulting or arising from:

(i) any change in general economic conditions in the industries or markets in which the Acquired Assets are used;

(ii) seasonal reductions in revenues and/or earnings with respect to the Acquired Assets in the ordinary course of business;

(iii) national or international political conditions, including any engagement in hostilities, whether or not pursuant to the declaration of a national emergency or war, or the occurrence of any military or terrorist attack;

(iv) changes in Law or GAAP; and

(v) the entry into or announcement of this Agreement, actions contemplated by this Agreement, or the consummation of the transactions contemplated hereby.

Notwithstanding the foregoing clauses (i), (iii) and (iv) shall not apply in the event of a disproportionate effect on the Acquired Assets, as compared to other entities or assets in the markets in which the Acquired Assets are used.

“ Material Contracts ” has the meaning provided such term in Section 4.(7)(a).

“ MLP ” means SemGroup Energy Partners, L.P., a limited partnership organized under the Laws of the State of Delaware.

“ MLP GP ” means SemGroup Energy Partners G.P., L.L.C., a limited liability company organized under the Laws of the State of Delaware.

“ Obligations” shall mean duties, liabilities and obligations, whether vested, absolute or contingent, primary or secondary, direct or indirect, known or unknown, asserted or unasserted, accrued or unaccrued, liquidated or unliquidated, due or to become due, and whether contractual, statutory or otherwise.

“ Omnibus Agreement Amendment ” means that certain Amendment No. 1 to the Omnibus Agreement by and among Parent, SemManagement, SemMaterials, MLP, MLP GP and SMEP, substantially in the form of Exhibit D attached hereto.

“ Organizational Documents ” means any charter, certificate of incorporation, articles of association, certificate of limited partnership, bylaws, partnership agreement, operating agreement or similar formation or governing documents and instruments.

“ Parent ” means SemGroup, L.P., a limited partnership organized under the Laws of the State of Oklahoma.

“ Parent GP ” means SemGroup G.P., L.L.C., a limited liability company organized under the Laws of the State of Oklahoma.

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“ Party ” means Seller or Buyer, as the context so requires, and “ Parties ” means Seller and Buyer.

“ Permits ” means authorizations, licenses, permits or certifications issued by Governmental Authorities; provided , right-of-way agreements and similar rights and approvals are not included in the definition of Permits.

“ Permitted Liens ” means (a) Liens for Taxes not yet delinquent or being contested in good faith by appropriate proceedings, (b) statutory Liens (including materialmen’s, warehousemen’s, mechanic’s, repairmen’s, landlord’s and other similar Liens) arising in the ordinary course of business securing payments not yet delinquent or being contested in good faith by appropriate proceedings, (c) the rights of lessors and lessees under leases, and the rights of third parties under any agreement, in each case executed in the ordinary course of business, (d) the rights of licensors and licensees under licenses executed in the ordinary course of business, (e) restrictive covenants, easements and defects, imperfections or irregularities of title or Liens, if any, of a nature that do not have a Material Adverse Effect on the assets or properties subject thereto, (f) preferential purchase rights and other similar arrangements with respect to which consents or waivers are obtained for this transaction or as to which the time for asserting such rights has expired at the Closing Date without an exercise of such rights, (g) restrictions on transfer with respect to which consents or waivers are obtained for this transaction, (h) Liens granted in the ordinary course of business which do not secure the payment of Indebtedness and which do not materially and adversely affect the ownership and operation of the Acquired Assets, (i) Liens which are of a nature that would be reasonably acceptable to a prudent owner or operator of crude oil pipelines and storage facilities and facilities of a type similar to the Acquired Assets, (j) Liens listed in Schedule 1.1(vi) , and (k) Liens created by Buyer or its successors and assigns.

“ Person ” means any individual, firm, corporation, partnership, limited liability company, incorporated or unincorporated association, joint venture, joint stock company, trust, Governmental Authority or other entity of any kind.

“ Personal Property ” has the meaning provided in Section 2.1(d) .

“ Pipeline ” means the Seller’s pipeline from the Ardmore, Oklahoma area, to the Drumright, Oklahoma area, as further described in Schedule 2.1(a) , and all appurtenances and facilities associated therewith.

“ Pre-Closing Environmental Liabilities ” means (i) any violation of Environmental Law by Seller or Seller’s Affiliates prior to the Effective Time or arising in connection with the ownership or operation of the Acquired Assets prior to the Effective Time, (ii) any Release of Hazardous Substances onto or from the Acquired Assets prior to the Effective Time or relating to or arising from any activities conducted on such properties or from operation of such assets prior to the Effective Time and (iii) any claim, action, cause of action, inquiry, investigation, remediation, removal or restoration with respect to the matters set forth in subsection (i) or (ii) above.

“ Purchase Price ” has the meaning provided such term in Section 2.3 .

“ Real Property ” has the meaning provided such term in Section 2.1(b) .

“ Reasonable Efforts ” means efforts in accordance with reasonable commercial practice and without the incurrence of unreasonable expense.

“ Records ” means all of Seller’s accounts, books (financial and otherwise), and all operational technical records in any way relating to the ownership and operation of the Assets prior to the Effective

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Time, including: non-proprietary design manuals, operation and safety manuals, blueprints, engineering studies and engineering reports, object code (with respect to computer software), user operations and system documentation, system engineering and design information, and all associated data files and databases to the extent such systems exist for the operation of the Acquired Assets and can be delivered by Seller to Buyer. Records specifically excludes (i) personnel and employment records of employees, (ii) records, documents, plans, strategies and financial records related to the transactions contemplated by this Agreement, and (iii) any of Seller’s or Seller’s Affiliates minute books and records, Tax returns or other materials which do not pertain to the Acquired Assets or the business conducted by Seller utilizing the Acquired Assets or any part thereof.

“ Release ” means any depositing, spilling, leaking, pumping, pouring, placing, emitting, discarding, abandoning, emptying, discharging, migrating, injecting, escaping, leaching, dumping, or disposing.

“ Representatives ” means, as to any Person, its officers, directors, employees, counsel, accountants, financial advisers and consultants.

“ Required Governmental Consents ” has the meaning provided such term in Section 7.1(h) .

“ Retained Obligations ” has the meaning provided such term in Section 2.6(b) .

“ Rights-of-Way ” has the meaning provided such term in Section 2.1(c) .

“ Seller ” has the meaning provided such term in the preamble to this Agreement.

“ Seller Ancillary Document ” means each agreement, document or certificate to be delivered by Seller at Closing pursuant to Section 2.4(b) .

“ Seller Approvals ” has the meaning provided such term in Section 3.3 .

“ Seller Entities ” means Parent, SemManagement, SemMaterials, Seller and Eaglwing.

“ Seller Indemnified Parties ” has the meaning provided such term in Section 8.2(b) .

“ SemManagement ” means SemManagement, L.L.C., a limited liability company organized under the Laws of the State of Delaware.

“ SemMaterials ” means SemMaterials L.P., a limited partnership organized under the Laws of the State of Oklahoma.

“ SMEP ” means SemMaterials Energy Partners, L.L.C., a limited liability company organized under the Laws of the State of Delaware.

“ Subsidiary ” means, with respect to any Person, (a) any corporation 50% or more of whose stock of any class or classes having by the terms thereof ordinary voting power to elect a majority of the directors of such corporation (irrespective of whether or not at the time stock of any class or classes of such corporation have or might have voting power by reason of the happening of any contingency) is at the time owned by such Person, directly or indirectly through Subsidiaries, and (b) any partnership, limited liability company, association, joint venture, trust or other entity in which such Person, directly or indirectly through Subsidiaries has a 50% or greater equity interest at the time.

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“ Tax Authority ” means any Governmental Authority having jurisdiction over the assessment, determination, collection or imposition of any Tax.

“ Tax Returns ” means any report, return, election, document, estimated tax filing, declaration or other filing provided to any Tax Authority including any amendments thereto.

“ Taxes ” or “ Tax ” means (a) all taxes, assessments, duties, levies, imposts or other similar charges imposed by a Governmental Authority, including all income, franchise, profits, capital gains, capital stock, transfer, gross receipts, sales, use, transfer, service, occupation, ad valorem, property, excise, severance, windfall profits, premium, stamp, license, payroll, employment, social security, unemployment, disability, environmental (including taxes under Code Section 59A), alternative minimum, add-on, value-added, withholding (including backup withholding) and other taxes, assessments, duties, levies, imposts or other similar charges of any kind whatsoever (whether payable directly or by withholding and whether or not requiring the filing of a Tax Return), and all estimated taxes, deficiency assessments, additions to tax, additional amounts imposed by any Governmental Authority, penalties and interest, and (b) any liability for the payment of any amounts of any of the foregoing types as a result of being a member of an affiliated, consolidated, combined or unitary group, or being a party to any agreement or arrangement whereby liability of Seller for payment of such amounts was determined or taken into account with reference to the liability of any other Person.

“ Third-Party Claim ” has the meaning provided such term in Section 8.3(a) .

“ Third-Party Equipment ” means any and all real and personal property, whether located at or on the Real Property or otherwise, belonging to third parties and not owned by Seller.

“ Third Person Receivables ” has the meaning provided such term in Section 2.5(c) .

“ Throughput Agreement Amendment ” means that certain Amendment No. 1 to the Throughput Agreement among Parent, Eaglwing, Seller, MLP and Buyer, in the form of Exhibit E attached hereto.

“ United States ” means United States of America.

Section 1.2 Rules of Construction.

(a) All article, section, schedule and exhibit references used in this Agreement are to articles, sections, schedules and exhibits to this Agreement unless otherwise specified. The schedules and exhibits attached to this Agreement constitute a part of this Agreement and are incorporated herein for all purposes.

(b) If a term is defined as one part of speech (such as a noun), it shall have a corresponding meaning when used as another part of speech (such as a verb). Terms defined in the singular have the corresponding meanings in the plural, and vice versa. Unless the context of this Agreement clearly requires otherwise, words importing the masculine gender shall include the feminine and neutral genders and vice versa. The term “includes” or “including” shall mean “including without limitation.” The words “hereof,” “hereto,” “hereby,” “herein,” “hereunder” and words of similar import, when used in this Agreement, shall refer to this Agreement as a whole and not to any particular section or article in which such words appear.

(c) The Parties acknowledge that each Party and its attorney has reviewed this Agreement and that any rule of construction to the effect that any ambiguities are to be resolved against the drafting Party, or any similar rule operating against the drafter of an agreement, shall not be applicable to the construction or interpretation of this Agreement.

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(d) The captions in this Agreement are for convenience only and shall not be considered a part of or affect the construction or interpretation of any provision of this Agreement.

(e) All references to currency herein shall be to, and all payments required hereunder shall be paid in, Dollars.

(f) All accounting terms used herein and not expressly defined herein shall have the meanings given to them under GAAP.

(g) Any event hereunder requiring the payment of cash or cash equivalents on a day that is not a Business Day shall be deferred until the next Business Day.

ARTICLE II

PURCHASE AND SALE; CLOSING

Section 2.1 Purchase and Sale of Acquired Assets . On the Closing Date, but effective as of the Effective Time and subject to the terms and conditions set forth in this Agreement, Seller shall sell, assign, transfer and convey to Buyer, and Buyer shall purchase and acquire from Seller, all of Seller’s right, title and interest in the assets described in this Section 2.1 (collectively, the “ Acquired Assets ”), free and clear of any and all Liens other than Permitted Liens:

(a) the Pipeline;

(b) the tracts and parcels of real estate owned in fee by Seller as described in Schedule 2.1(b) (the “ Land ”) together with (i) all buildings and other structures, facilities or improvements currently or hereafter located thereon and permanently affixed thereto; (ii) all fixtures, systems, owned or leased equipment and other items of tangible personal property situated thereon or attached thereto; and (iii) all easements, licenses, rights and appurtenances relating to the property described in the foregoing clauses (the Land, together with the property and assets described in the foregoing clauses (i) though (iii) referred to herein as the “ Real Property ”);

(c) the real property leased by Seller from a third party (the “ Leases ”) and the easements, rights of way, permits, licenses and any other type of real property use agreement in which Seller has rights or any interest and which is held by Seller for use with respect to the assets described in this Section (the “ Rights-of-Way ”), in each case, including, without limitation, those certain Leases and Rights-of-Way described in Schedule 2.1(c) ;

(d) the tangible assets owned by Seller and located on the Real Property or used primarily in connection with the Pipeline which do not constitute Real Property or Rights of Way, including such tangible assets described in Schedule 2.1(a) (the “ Personal Property ”);

(e) the Records;

(f) the Material Contracts; and

(g) all other assets or rights used in connection with the Acquired Assets or located at the Acquired Assets other than Excluded Assets or rights associated with the Retained Obligations.

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Section 2.2 [INTENTIONALLY OMITTED]

Section 2.3 Purchase Price . The consideration payable by Buyer to Seller for the Acquired Assets shall be Forty-Five Million Dollars ($45,000,000) (the “Purchase Price” ). Payment of the Purchase Price shall be made by wire transfer or delivery of other immediately available funds on the Closing Date to a bank account designated in writing by Seller to Buyer at least 2 Business Days prior to Closing.

Section 2.4 The Closing.

(a) The closing of the transactions contemplated by this Agreement (the “ Closing ”) shall take place at the offices of Hall, Estill, Hardwick, Gable, Golden & Nelson, P.C., 320 South Boston Avenue, Suite 200, Tulsa, Oklahoma 74103-3708, commencing at 11:00 a.m. as of the date hereof (the “ Closing Date ”); provided , the Closing shall be deemed to have been consummated at 12:01 a.m. Tulsa, Oklahoma time on the Closing Date (the “ Effective Time ”).

(b) At the Closing, Seller will deliver the following documents and deliverables to Buyer:

(i) one or more properly executed and acknowledged special warranty deeds (the “ Deeds ”) conveying to Buyer good and marketable title to the Real Property, each such Deed to be substantially in the form of Exhibit F . The Deeds shall be in recordable form for recording the Deeds in the county in which the Real Property is located;

(ii) a duly executed counterpart by Seller of the Assignment and Assumption of Leases and Rights-of-Way substantially in the form of Exhibit B conveying to Buyer all of Seller’s right, title and interest in the Leases and the Rights-of-Way;

(iii) a duly executed counterpart by Seller of the Assignment and Assumption Agreement substantially in the form of Exhibit A conveying to Buyer the Material Contracts;

(iv) a duly executed counterpart by Seller of the Bill of Sale substantially in the form of Exhibit C attached hereto, conveying to Buyer the Personal Property;

(v) a duly executed counterpart of Omnibus Agreement Amendment, substantially in the form of Exhibit D attached hereto, duly executed by Parent, SemManagement and SemMaterials;

(vi) a duly executed counterpart of the Throughput Agreement Amendment, substantially in the form of Exhibit E attached hereto, duly executed by Seller, Parent and Eaglwing;

(vii) certificates of good standing and existence from the Secretary of State of Delaware as of a recent date with respect to Seller; and

(viii) such other certificates, instruments of conveyance and documents as may be reasonably requested by Buyer prior to the Closing Date to carry out the intent and purposes of this Agreement.

(c) At the Closing, Buyer will deliver the following documents and deliverables to Seller:

(i) an amount equal to the Purchase Price;

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(ii) a duly executed counterpart by Buyer of the Assignment and Assumption of Leases and Rights-of-Way substantially in the form of Exhibit B conveying to Buyer all of Seller’s right, title and interest in the Leases and the Rights-of-Way;

(iii) a duly executed counterpart by Buyer of the Assignment and Assumption Agreement substantially in the form