UNDERWRITING AGREEMENT

Exhibit 1.1

Execution Version

PLAINS ALL AMERICAN PIPELINE, L.P.

6,000,000 Common Units

Representing Limited Partner Interests

UNDERWRITING AGREEMENT

New York, New York
May 7, 2008

Wachovia Capital Markets, LLC
Citigroup Global Markets Inc.
UBS Securities LLC
Lehman Brothers Inc.
Merrill Lynch, Pierce, Fenner & Smith Incorporated
Morgan Stanley & Co. Incorporated
J.P. Morgan Securities, Inc.
Morgan Keegan & Company, Inc.
Oppenheimer & Co. Inc.
Raymond James & Associates, Inc.
RBC Capital Markets Corporation

c/o Wachovia Capital Markets, LLC
1001 Fannin Street, Suite 2255
Houston, Texas 77002

Dear Sirs:

          Plains All American Pipeline, L.P., a Delaware limited partnership (the “ Partnership ”), proposes to issue and sell an aggregate of 6,000,000 common units (the “ Firm Units ”) representing limited partner interests in the Partnership (“ Common Units ”) to the several underwriters named in Schedule I hereto (the “ Underwriters ”), upon the terms and conditions set forth in Section 2 hereof. The Partnership also proposes to grant to the Underwriters, upon the terms and conditions set forth in Section 2 hereof, an option to purchase up to an additional 900,000 Common Units (the “ Option Units ”). The Firm Units and the Option Units are hereinafter collectively called the “ Units .”

          PAA GP LLC, a Delaware limited liability company (the “ General Partner ”), is the general partner of the Partnership. Plains AAP, L.P., a Delaware limited partnership (“ Plains AAP ”), owns a 100% membership interest in the General Partner. Plains All American GP LLC, a Delaware limited liability company (“ GP LLC ”), is the general partner of Plains AAP.

          Plains Marketing GP Inc., a Delaware corporation (“ GP Inc. ”); Plains Marketing, L.P., a Texas limited partnership (“ Plains Marketing ”); Plains Pipeline, L.P., a Texas limited partnership (“ Plains Pipeline ”); Pacific Energy Group LLC, a Delaware limited liability company (“ Pacific Energy Group ”); PAA Finance Corp., a Delaware corporation; Pacific Energy Finance Corporation, a Delaware corporation; Pacific LA Marine Terminal LLC, a Delaware limited liability company; Rocky Mountain Pipeline System LLC, a Delaware limited liability company; Pacific Atlantic Terminals LLC, a Delaware limited liability company; Ranch Pipeline LLC, a Delaware limited liability company; Plains Towing LLC, a Delaware limited liability company; Plains Marketing Canada LLC, a Delaware limited liability company (“ PMC LLC ”); Plains LPG Services GP LLC, a Delaware limited liability company (“ LPG LLC ”); PICSCO LLC, a Delaware limited liability company; Plains LPG Services, L.P., a Delaware limited partnership (“ LPG Services LP ”); Plains Midstream GP LLC, a Delaware limited liability company (“ Plains Midstream GP ”); Plains Midstream, L.P., a Delaware limited partnership (“ Plains Midstream LP ”); Lone Star Trucking, LLC, a California limited liability company; Basin Holdings GP LLC, a Delaware limited liability company (“ Basin LLC ”); Basin Pipeline Holdings, L.P., a Delaware limited partnership (“ Basin LP ”); Rancho Holdings GP LLC, a Delaware limited liability company (“ Rancho LLC ”); and Rancho Pipeline Holdings, L.P., a Delaware limited partnership (“ Rancho LP ”), are collectively referred to herein as the “ Domestic Subsidiaries .”

          Aurora Pipeline Company Ltd., a corporation incorporated under the laws of Canada ( “Aurora ”); Plains Midstream Canada ULC, an Alberta unlimited liability company (“ Plains Midstream Canada ”); Plains Marketing Canada, L.P., an Alberta limited partnership (“ PMC LP ”); and PMC (Nova Scotia) Company, a Nova Scotia unlimited liability company (“ PMC NS ”), are collectively referred to herein as the “ Canadian Subsidiaries .”

          Andrews Partners, LLC, a California limited liability company; Pacific Energy GP, LP, a Delaware limited partnership; Pacific Energy Management LLC, a Delaware limited liability company; Pacific Pipeline System LLC, a Delaware limited liability company; Pacific Terminals LLC, a Delaware limited liability company; SLC Pipeline LLC, a Delaware limited liability company; PEG Canada GP LLC, a Delaware limited liability company; 1366390 Alberta ULC, an Alberta unlimited liability company; Rangeland Marketing Company, a Nova Scotia unlimited liability company; Rangeland Pipeline Company, a Nova Scotia unlimited liability company; Rangeland Northern Pipeline Company, a Nova Scotia unlimited liability company; and Plains All American Emergency Relief Fund, a Delaware corporation, are collectively referred to herein as the “ Other Subsidiaries .”

          The Domestic Subsidiaries and the Canadian Subsidiaries are collectively referred to herein as the “Subsidiaries .” The Partnership, the General Partner, Plains AAP, GP LLC, GP Inc., Plains Marketing, Plains Pipeline and Pacific Energy Group are collectively referred to herein as the “ Plains Parties .” The Partnership, the General Partner, Plains AAP, GP LLC, the Subsidiaries, the Other Subsidiaries and PAA/Vulcan Gas Storage, LLC, a Delaware limited liability company (the “ Joint Venture ”), are collectively referred to herein as the “ Plains Entities .”

          The Plains Parties wish to confirm as follows their agreement with you in connection with the several purchases of the Units by the Underwriters.

          1. Representations and Warranties of the Plains Parties . The Plains Parties, jointly and severally, represent and warrant to the Underwriters that:

          (a) A registration statement on Form S-3 relating to the Units (File No. 333-126447) (i) has been prepared by the Partnership in conformity with the requirements of the Securities Act of 1933, as amended (the “ Securities Act ”), and the rules and regulations (the “ Rules and Regulations ”) of the Securities and Exchange Commission (the “ Commission ”) thereunder; (ii) has been filed with the Commission under the Securities Act; and (iii) is effective under the Securities Act. Copies of such registration statement and any amendment thereto have been delivered by the Partnership to you as the representatives of the Underwriters (the “ Representatives ”). As used in this Agreement:

     (i) “ Applicable Time ” means 8:45 a.m., New York City time, on May 7, 2008, which the Underwriters have informed the Partnership and its counsel is a time prior to the first sale of the Units;

     (ii) “ Effective Date ” means any date as of which any part of such registration statement relating to the Units became, or is deemed to have become, effective under the Securities Act in accordance with the Rules and Regulations;

     (iii) “ Issuer Free Writing Prospectus ” means each “free writing prospectus” (as defined in Rule 405 of the Rules and Regulations) prepared by or on behalf of the Partnership or used or referred to by the Partnership in connection with the offering of the Units;

     (iv) “ Preliminary Prospectus ” means any preliminary prospectus relating to the Units included in such registration statement or filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations, including any preliminary prospectus supplement thereto relating to the Units;

     (v) “ Pricing Disclosure Package ” means, as of the Applicable Time, the most recent Preliminary Prospectus, together with (A) each Issuer Free Writing Prospectus filed or used by the Partnership on or before the Applicable Time, other than a road show that is an Issuer Free Writing Prospectus under Rule 433 of the Rules and Regulations, and (B) the final term sheet attached hereto as Schedule II ;

     (vi) “ Prospectus ” means the final prospectus relating to the Units, including any prospectus supplement thereto relating to the Units, as filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations; and

     (vii) “ Registration Statement ” means the registration statement on Form S-3 (File No. 333-126447), as amended as of the Effective Date, including any Preliminary Prospectus or the Prospectus and all exhibits to such registration statement.

     Any reference to any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any documents incorporated by reference therein pursuant to Form S-3 under the Securities Act as of the date of such Preliminary Prospectus or the Prospectus, as the case may

be. Any reference to the “ most recent Preliminary Prospectus ” shall be deemed to refer to the latest Preliminary Prospectus included in the Registration Statement or filed pursuant to Rule 424(b) of the Rules and Regulations prior to or on the date hereof (including, for purposes hereof, any documents incorporated by reference therein prior to or on the date hereof). Any reference to any amendment or supplement to any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any document filed under the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), after the date of such Preliminary Prospectus or the Prospectus, as the case may be, and incorporated by reference in such Preliminary Prospectus or the Prospectus, as the case may be. Any reference to any amendment to the Registration Statement shall be deemed to include any periodic report of the Partnership filed with the Commission pursuant to Section 13(a) or 15(d) of the Exchange Act after the Effective Date that is incorporated by reference in the Registration Statement. As used herein, the term “ Incorporated Documents ” means the documents that at the time are incorporated by reference in the Registration Statement, the Preliminary Prospectus or the Prospectus or any amendment or supplement thereto. The Commission has not issued any order preventing or suspending the use of any Preliminary Prospectus or the Prospectus or suspending the effectiveness of the Registration Statement, and no proceeding for such purpose has been instituted or, to the Plains Parties’ knowledge, threatened by the Commission. The Commission has not notified the Partnership of any objection to the use of the form of the Registration Statement.

          (b) The Registration Statement conformed and will conform in all material respects on the Effective Date and on each applicable Delivery Date (as defined herein), and any amendment to the Registration Statement filed after the date hereof will conform in all material respects when filed, to the requirements of the Securities Act and the Rules and Regulations. The most recent Preliminary Prospectus conformed, and the Prospectus will conform, in all material respects when filed with the Commission pursuant to Rule 424(b) and on each applicable Delivery Date to the requirements of the Securities Act and the Rules and Regulations. The Incorporated Documents conformed and will conform, when filed with the Commission, in all material respects to the requirements of the Exchange Act or the Securities Act, as applicable, and the rules and regulations of the Commission thereunder.

          (c) The Registration Statement did not, as of its most recent Effective Date, 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 not misleading; provided that no representation or warranty is made as to information contained in or omitted from the Registration Statement in reliance upon and in conformity with written information furnished to the Partnership through the Representatives by or on behalf of any Underwriter specifically for inclusion therein, which information is specified in Section 12.

          (d) The Prospectus will not, as of its date and on the applicable Delivery Date, contain an 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; provided that no representation or warranty is made as to information contained in or omitted from the Prospectus in reliance upon and in conformity with written information furnished to the Partnership through the Representatives by or on behalf of any Underwriter specifically for inclusion therein, which information is specified in Section 12.

          (e) The Incorporated Documents, when filed with the Commission, conformed or will conform, as the case may be, in all material respects to the applicable requirements of the Exchange Act and the Rules and Regulations, and did not and will not contain an 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.

          (f) The Pricing Disclosure Package did not, as of the Applicable Time, contain an 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; provided that no representation or warranty is made as to information contained in or omitted from the Pricing Disclosure Package in reliance upon and in conformity with written information furnished to the Partnership through the Representatives by or on behalf of any Underwriter specifically for inclusion therein, which information is specified in Section 12.

          (g) Each Issuer Free Writing Prospectus (including, without limitation, any road show that is a free writing prospectus under Rule 433 of the Rules and Regulations), when considered together with the Pricing Disclosure Package as of the Applicable Time, did not contain an 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.

          (h) Each Issuer Free Writing Prospectus conformed or will conform in all material respects to the requirements of the Securities Act and the Rules and Regulations on the date of first use, and the Partnership has complied with any filing requirements applicable to such Issuer Free Writing Prospectus pursuant to the Rules and Regulations. The Partnership has not made any offer relating to the Units that would constitute an Issuer Free Writing Prospectus without the prior written consent of the Representatives. The Partnership has retained in accordance with the Rules and Regulations all Issuer Free Writing Prospectuses that were not required to be filed pursuant to the Rules and Regulations. The Partnership has taken all actions necessary so that any road show (as defined in Rule 433 of the Rules and Regulations) in connection with the offering of the Units will not be required to be filed pursuant to the Rules and Regulations.

          (i) At (i) the time of initial filing of the Registration Statement and (ii) the earliest time after the initial filing of the Registration Statement that the Partnership or another offering participant made a bona fide offer (within the meaning of Rule 164(h)(2) under the Securities Act) of the Units, the Partnership was not an “ineligible issuer,” as defined in Rule 405 under the Securities Act.

          (j) Each of the Partnership, the General Partner, Plains AAP, GP LLC, the Subsidiaries and the Joint Venture has been duly formed or incorporated and is validly existing in good standing as a limited partnership, limited liability company, corporation or unlimited liability company under the laws of its respective jurisdiction of formation or incorporation with full corporate, partnership, limited liability company or unlimited liability company power and authority, as the case may be, to own or lease its properties and to conduct its business, in each case in all material respects. Each of the Partnership, the General Partner, Plains AAP, GP LLC, the Subsidiaries and the Joint Venture is duly registered or qualified as a foreign corporation,

limited partnership, limited liability company or unlimited liability company, as the case may be, for the transaction of business under the laws of each jurisdiction (as set forth on Exhibit A to this Agreement) in which the character of the business conducted by it or the nature or location of the properties owned or leased by it makes such registration or qualification necessary, except where the failure so to register or qualify would not have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (k) GP LLC has full limited liability company power and authority to act as the general partner of Plains AAP; the General Partner has full limited liability company power and authority to act as the general partner of the Partnership; GP Inc. has full corporate power and authority to act as the general partner of Plains Marketing and Plains Pipeline; Basin LLC has full limited liability company power and authority to act as the general partner of Basin LP; Rancho LLC has full limited liability company power and authority to act as the general partner of Rancho LP; PMC NS has full unlimited liability company power and authority to act as the general partner of PMC LP; LPG LLC has full limited liability company power and authority to act as the general partner of LPG Services LP; and Plains Midstream GP has full limited liability company power and authority to act as the general partner of Plains Midstream LP, in each case in all material respects.

          (l) The General Partner is 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 Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same may be amended or restated prior to each applicable Delivery Date, the “ Partnership Agreement ”); and the General Partner owns such general partner interest free and clear of all liens, encumbrances, security interests, equities, charges or claims.

          (m) Plains AAP is the sole member of the General Partner, with a 100% membership interest in the General Partner; such membership interest has 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 prior to each applicable Delivery Date, such agreement being referred to herein as the “ General Partner LLC Agreement ”) and is fully paid (to the extent required under the General Partner LLC Agreement) and nonassessable (except as such nonassessability may be affected by matters described in Section 18-607 and 18-804 of the Delaware Limited Liability Company Act (the “ Delaware LLC Act ”)); and Plains AAP owns such membership interest free and clear of all liens, encumbrances, security interests, equities, charges or claims, except as provided in the Credit Agreement dated January 3, 2008 (as amended, the “ Plains AAP Facility ”), by and among Plains AAP, the lenders party thereto and Citibank, N.A., as Administrative Agent.

          (n) GP LLC is the sole general partner of Plains AAP, with a 1.0% general partner interest in Plains AAP; such general partner interest has been duly authorized and validly issued in accordance with the Fourth Amended and Restated Limited Partnership Agreement of Plains AAP (as the same may be amended or restated prior to each applicable Delivery Date, such agreement being referred to herein as the “ Plains AAP Partnership Agreement ”); and GP LLC owns such general partner interest free and clear of all liens, encumbrances, security interests, equities, charges or claims.

          (o) GP Inc. is the sole general partner of Plains Marketing, with a .001% general partner interest in Plains Marketing, and the sole general partner of Plains Pipeline, with a .001% general partner interest in Plains Pipeline; such general partner interests have been duly authorized and validly issued in accordance with the agreement of limited partnership of Plains Marketing and the agreement of limited partnership of Plains Pipeline, respectively (in each case, as in effect on the date hereof and as the same may be amended or restated prior to each applicable Delivery Date, such agreements being referred to herein as the “ Plains Marketing Partnership Agreement ” and the “ Plains Pipeline Partnership Agreement ,” respectively); and GP Inc. owns such general partner interests free and clear of all liens, encumbrances, security interests, equities, charges or claims.

          (p) As of the date hereof, the issued and outstanding partnership interests of the Partnership (other than the general partner interest) consist of 115,981,676 Common Units and the Incentive Distribution Rights (as such capitalized term is defined in the Partnership Agreement). All outstanding Common Units and Incentive Distribution Rights and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Section 17-607 of the Delaware Revised Uniform Limited Partnership Act (the “ Delaware LP Act ”)). The authorized limited partner interests of the Partnership conform as to legal matters to the descriptions thereof contained in the Pricing Disclosure Package and the Prospectus.

          (q) All of the outstanding shares of capital stock or other equity interests (other than general partner interests) of each Subsidiary, Other Subsidiary and the Joint Venture (a) have been duly authorized and validly issued (in the case of an interest in a limited partnership or limited liability company, in accordance with the Organizational Documents (as defined in Section 1(t) below) of such Subsidiary, Other Subsidiary or the Joint Venture), are fully paid (in the case of an interest in a limited partnership or limited liability company, to the extent required under the Organizational Documents of such Subsidiary, Other Subsidiary or the Joint Venture) and nonassessable (except (i) in the case of an interest in a Delaware limited partnership or Delaware limited liability company, as such nonassessability may be affected by Section 17-607 of the Delaware LP Act or Section 18-607 and 18-804 of the Delaware LLC Act), as applicable, (ii) in the case of an interest in a limited partnership or limited liability company formed under the laws of another domestic state, as such nonassessability may be affected by similar provisions of such state’s limited partnership or limited liability company statute, as applicable, and (iii) in the case of an interest in an entity formed under the laws of a foreign jurisdiction, as such nonassessability may be affected by similar provisions of such jurisdiction’s corporate, partnership or limited liability company statute, if any, as applicable) and (b) except for a 50% membership interest in the Joint Venture owned by Vulcan Gas Storage LLC, are owned, directly or indirectly, by the Partnership, free and clear of all liens, encumbrances, security interests, equities, charges or claims.

          (r) All outstanding general partner interests in each Subsidiary that is a partnership have been duly authorized and validly issued in accordance with the Organizational Documents of such Subsidiary and are owned, directly or indirectly, by the Partnership, free and clear of all liens, encumbrances, security interests, equities, charges or claims.

          (s) At the applicable Delivery Date, the Units to be sold by the Partnership and the limited partner interests represented thereby will be duly authorized in accordance with the Partnership Agreement and, when issued and delivered to the Underwriters against payment therefor in accordance with the terms hereof, will be validly issued, fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Section 17-607 of the Delaware LP Act).

          (t) Except as described in the Pricing Disclosure Package and the Prospectus or as provided in the Organizational Documents (as defined below), there are no preemptive rights or other rights to subscribe for or to purchase, nor any restriction upon the voting or transfer of, any interests in the Partnership, the General Partner, Plains AAP, the Subsidiaries or the Joint Venture pursuant to the agreement or certificate of limited partnership, limited liability company agreement, certificate of formation, certificate or articles of incorporation, bylaws or other similar organizational documents (in each case as in effect on the date hereof and as the same may be amended or restated prior to each applicable Delivery Date) (the “ Organizational Documents ”) of the Partnership, the General Partner, Plains AAP, the Subsidiaries or the Joint Venture or any agreement or other instrument to which the Partnership, the General Partner, Plains AAP, the Subsidiaries or the Joint Venture is a party or by which any one of them may be bound. 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, the General Partner, Plains AAP, the Subsidiaries or the Joint Venture, except such rights as have been waived or satisfied. Except as described in the Pricing Disclosure Package and the Prospectus, there are no outstanding options or warrants to purchase any Common Units or other equity interests in the Partnership, the General Partner, Plains AAP, the Subsidiaries or the Joint Venture. The Units, when issued and delivered against payment therefor as provided herein, will conform in all material respects to the description thereof contained in the Pricing Disclosure Package and the Prospectus.

          (u) The Partnership has all requisite power and authority to issue, sell and deliver the Units, in accordance with and upon the terms and conditions set forth in this Agreement, the Partnership Agreement and the Registration Statement, the Pricing Disclosure Package and the Prospectus. At each applicable Delivery Date, all corporate, limited liability company and partnership action, as the case may be, required to be taken by the Partnership or its partners for the authorization, issuance, sale and delivery of the Units shall have been validly taken.

          (v) The execution and delivery of, and the performance by each of the Plains Parties of their respective obligations under, this Agreement have been duly and validly authorized by each of the Plains Parties, and this Agreement has been duly executed and delivered by each of the Plains Parties, and constitutes the valid and legally binding agreement of each of the Plains Parties, enforceable against each of the Plains Parties in accordance with its terms; provided that the enforceability hereof 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) and except as rights to indemnity and contribution hereunder may be limited by federal or state securities laws.

(w) (i) The General Partner LLC Agreement has been duly authorized, executed and delivered by Plains AAP and is a valid and legally binding agreement of Plains AAP, enforceable against it in accordance with its terms;

     (ii) the Plains AAP Partnership Agreement has been duly authorized, executed and delivered by GP LLC and Plains AAP’s limited partners and, assuming due authorization, execution and delivery by the other parties thereto, is a valid and legally binding agreement of GP LLC and such limited partners, enforceable against the GP LLC and such limited partners in accordance with its terms;

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

     (iv) the Plains Marketing Partnership Agreement has been duly authorized, executed and delivered by each of GP Inc. and the Partnership, and is a valid and legally binding agreement of GP Inc. and the Partnership, enforceable against each of them in accordance with its terms;

     (v) the Plains Pipeline Partnership Agreement has been duly authorized, executed and delivered by each of GP Inc. and Plains Marketing and is a valid and legally binding agreement of GP Inc. and Plains Marketing, enforceable against each of them in accordance with its terms;

     (vi) the Limited Liability Company Agreement of Pacific Energy Group (as in effect on the date hereof and as the same may be amended or restated prior to each applicable Delivery Date, the “ Pacific Energy Group 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 it in accordance with its terms; and

     (vii) the Limited Liability Company Agreement of the Joint Venture (as in effect on the date hereof and as the same may be amended or restated prior to each applicable Delivery Date, the “ Gas Storage LLC Agreement ”) has been duly authorized, executed and delivered by the Partnership and, assuming due authorization, execution and delivery by the other parties thereto, is a valid and legally binding agreement of the Partnership, enforceable against it in accordance with its terms;

provided that, with respect to each such agreement, 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).

          (x) None of the offering, issuance and sale by the Partnership of the Units, the execution, delivery and performance of this Agreement by the Plains Parties, or the consummation of the transactions contemplated hereby (i) conflicts or will conflict with or

constitutes or will constitute a violation of the Organizational Documents of any of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries, (ii) conflicts or will conflict with or constitutes or will constitute a breach or violation of, a change of control or a default under (or an event which, with notice or lapse of time or both, would constitute such an event), any indenture, mortgage, deed of trust, loan agreement, lease or other agreement or instrument to which any of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries is a party or by which any of them or any of their respective properties may be bound, (iii) 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 Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries or any of their properties in a proceeding to which any of them or their property is a party or (iv) will result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of any of the Partnership, the General Partner, Plains AAP, GP LLC, the Subsidiaries or the Joint Venture, which conflicts, breaches, violations or defaults, in the case of clauses (ii), (iii) or (iv), would have a material adverse effect upon the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (y) No permit, consent, approval, authorization, order, registration, filing or qualification of or with any court, governmental agency or body is required in connection with the offering, issuance and sale by the Partnership of the Units, the execution, delivery and performance of, or the consummation by the Plains Parties of the transactions contemplated by, this Agreement, except for such permits, consents, approvals and similar authorizations required under the Securities Act, the Exchange Act and state securities or “Blue Sky” laws.

          (z) None of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries is in (i) violation of its Organizational Documents, or of any law, statute, ordinance, administrative or governmental rule or regulation applicable to it or of any decree of any court or governmental agency or body having jurisdiction over it or (ii) breach, default (or an event that, 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 bond, debenture, note or any other evidence of indebtedness or in any agreement, indenture, lease or other instrument to which it is a party or by which it or any of its properties may be bound, which breach, default or violation would, if continued, have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole, or could materially impair the ability of any of the Plains Parties to perform its obligations under this Agreement. To the knowledge of the Plains Parties, no third party to any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which any of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries is a party or by which any of them is bound or to which any of their properties are subject, is in default under any such agreement, which breach, default or violation would, if continued, have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (aa) The accountants, PricewaterhouseCoopers LLP, who have certified or shall certify the audited financial statements included in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus (and any amendment or supplement thereto), are independent registered public accountants with respect to the Partnership, the General Partner and the Subsidiaries as required by the Securities Act and the Rules and Regulations.

          (bb) At March 31, 2008, the Partnership would have had, on an as adjusted basis as indicated in the Prospectus (and any amendment or supplement thereto), a total capitalization as set forth therein. The financial statements (including the related notes and supporting schedules) and other financial information included in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus (and any amendment or supplement thereto) present fairly in all material respects the financial position, results of operations and cash flows of the entities purported to be shown thereby, at the dates and for the periods indicated, and have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods indicated, except to the extent disclosed therein. The summary and selected historical financial information included or incorporated by reference in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus (and any amendment or supplement thereto) is accurately presented in all material respects and prepared on a basis consistent with the audited and unaudited historical consolidated financial statements from which it has been derived, except as described therein. The pro forma financial statements and other pro forma financial information, if any, included or incorporated by reference in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus (and any amendment or supplement thereto) (i) present fairly in all material respects the information shown therein, (ii) have been prepared in accordance with the Commission’s rules and guidelines with respect to pro forma financial statements and (iii) have been properly computed on the bases described therein. The assumptions used in the preparation of the pro forma financial statements and other pro forma financial information, if any, included or incorporated by reference in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus (and any amendment or supplement thereto) are reasonable, and the adjustments used therein are appropriate to give effect to the transactions or circumstances referred to therein. No other financial statements or schedules of the Partnership are required by the Securities Act or the Exchange Act to be included in the Registration Statement, the most recent Preliminary Prospectus or the Prospectus.

          (cc) The Partnership’s acquisition, through Plains Midstream Canada, of Rainbow Pipe Line Company, Ltd. for approximately Can$540 million, as described in the most recent Preliminary Prospectus and the Prospectus, will not require the filing by the Partnership with the Commission of acquisition financial statements pursuant to Rule 3-05 of Regulation S-X of the Exchange Act.

          (dd) Except as disclosed in the Pricing Disclosure Package and the Prospectus, subsequent to the respective dates as of which such information is given in the Pricing Disclosure Package and the Prospectus, (i) none of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries has incurred any liability or obligation, indirect, direct or contingent, or entered into any transactions, not in the ordinary course of business, that, singly or in the aggregate, is material to the Plains Entities, taken as a whole, (ii) there has not been any material change in the capitalization, or material increase in the short-term debt or long-term debt, of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries and (iii) there has not been any material adverse change, or any development involving or which may reasonably be expected to involve, singly or in the aggregate, a prospective material adverse change in the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (ee) There are no legal or governmental proceedings pending or, to the knowledge of the Plains Parties, threatened, against any of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries, or to which any of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries is a party, or to which any of their respective properties is subject, that are required to be described in the Registration Statement, the Pricing Disclosure Package or the Prospectus but 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, the Pricing Disclosure Package or the Prospectus or to be filed as an exhibit to the Registration Statement that are not described or filed as required by the Securities Act or the Exchange Act.

          (ff) The Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries have good and indefeasible title to all real property and good title to all personal property described in the Pricing Disclosure Package and the Prospectus as being owned by them, free and clear of all liens, claims, security interests or other encumbrances except (i) as provided in the Restated Credit Agreement (Uncommitted Senior Secured Discretionary Contango Facility) dated November 19, 2004 (as amended, the “ Contango Credit Agreement ”) among Plains Marketing, Bank of America, N.A., as administrative agent thereunder and the lenders from time to time party thereto, described in the Pricing Disclosure Package and the Prospectus, (ii) as provided in the Plains AAP Facility, and (iii) such as do not materially interfere with the use of such properties taken as a whole as described in the Pricing Disclosure Package and the Prospectus; and all real property and buildings held under lease by any of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries are held under valid and subsisting and enforceable leases with such exceptions as do not materially interfere with the use of such properties taken as a whole as described in the Pricing Disclosure Package and the Prospectus.

          (gg) Each of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has such permits, consents, licenses, franchises, certificates and authorizations of governmental or regulatory authorities (“ permits ”) as are necessary to own its properties and to conduct its business in the manner described in the Pricing Disclosure Package and the Prospectus, subject to such qualifications as may be set forth in the Pricing Disclosure Package and the Prospectus and except for such permits the failure of which to have obtained would not have, individually or in the aggregate, a material adverse effect upon the ability of the Plains Entities considered as a whole to conduct their businesses in all material respects as currently conducted and as contemplated by the Pricing Disclosure Package and the Prospectus to be conducted; each of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has fulfilled and performed all of its material obligations with respect to such permits and no event has occurred that allows, or after notice or lapse of time would allow, revocation or termination thereof or results in any impairment of the rights of the holder of any such permit, except for such failures to perform, revocations, terminations and impairments that would not have a material adverse effect upon the ability of the Plains Entities considered as a whole to conduct their businesses in all material respects as currently conducted and as contemplated by the Pricing Disclosure Package and the Prospectus to be conducted, subject in each case to such qualification as may be set forth in the Pricing Disclosure Package and the Prospectus; and, except as described in the Pricing Disclosure Package and the Prospectus, none of such permits contains any restriction that is materially burdensome to Plains Entities, considered as a whole.

          (hh) Each of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has such consents, easements, rights-of-way or licenses from any person (“ rights-of-way ”) as are necessary to conduct its business in the manner described in the Pricing Disclosure Package and the Prospectus, subject to such qualifications as may be set forth in the Pricing Disclosure Package and the Prospectus and except for such rights-of-way the failure of which to have obtained would not have, individually or in the aggregate, a material adverse effect upon the ability of the Plains Entities considered as a whole to conduct their businesses in all material respects as currently conducted and as contemplated by the Pricing Disclosure Package and the Prospectus to be conducted; each of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has fulfilled and performed all its 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 failures to perform, revocations, terminations and impairments that will not have a material adverse effect upon the ability of the Plains Entities considered as a whole to conduct their businesses in all material respects as currently conducted and as contemplated by the Pricing Disclosure Package and the Prospectus to be conducted, subject in each case to such qualification as may be set forth in the Prospectus; and, except as described in the Pricing Disclosure Package and the Prospectus, none of such rights-of-way contains any restriction that is materially burdensome to the Plains Entities, considered as a whole.

          (ii) None of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries is now, and after sale of the Units to be sold by the Partnership hereunder and application of the net proceeds from such sale as described in the Pricing Disclosure Package and the Prospectus under the caption “Use of Proceeds,” none of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries will be, (i) an “investment company” or a company “controlled by” an “investment company” within the meaning of the Investment Company Act of 1940, as amended, (ii)  a “gas utility,” within the meaning of Tex. Util. Code § 121.001 or (iii) a “public utility” or “utility” within the meaning of the Public Utility Regulatory Act of Texas or under similar laws of any state in which any such Plains Party does business; other than in respect of any subsidiary of Pacific Energy Group that is under the jurisdiction of the California Public Utility Commission.

          (jj) None of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has sustained since the date of the latest audited financial statements included in the Pricing Disclosure Package and the Prospectus (and any amendment or supplement thereto) any material loss or interference with its business from fire, explosion, flood or other calamity whether or not covered by insurance, or from any labor dispute or court or governmental action, investigation, order or decree, otherwise than as set forth or contemplated in the Pricing Disclosure Package and the Prospectus (and any amendment or supplement thereto), which in each case would have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (kk) Except as described in the Pricing Disclosure Package and the Prospectus, none of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has violated any environmental, safety, health or similar law or regulation applicable to its business relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (“ Environmental Laws ”), or lacks any permits,

licenses or other approvals required of them under applicable Environmental Laws to own, lease or operate their properties and conduct their business as described in the Pricing Disclosure Package and the Prospectus or is violating any terms and conditions of any such permit, license or approval, which in each case would have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (ll) No labor dispute by the employees of any of the Partnership, the General Partner, Plains AAP, GP LLC or the Subsidiaries exists or, to the knowledge of the Plains Parties, is imminent, which might reasonably be expected to have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole.

          (mm) The Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries maintain insurance covering their properties, operations, personnel and businesses against such losses and risks as are reasonably adequate to protect them and their businesses in a manner consistent with other businesses similarly situated. None of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has received notice from any insurer or agent of such insurer that substantial capital improvements or other expenditures will have to be made in order to continue such insurance, and all such insurance is outstanding and duly in force on the date hereof and will be outstanding and duly in force on each applicable Delivery Date.

          (nn) Except as described in the Pricing 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 the Plains Parties, threatened, to which any of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries, or any of their respective subsidiaries, is or may be a party or to which the business or property of any of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries, or any of their respective subsidiaries, is or may be subject, (ii) no statute, rule, regulation or order that has been enacted, adopted or issued by any governmental agency or, to the knowledge of the Plains Parties, that has been proposed by any governmental body 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, the General Partner, Plains AAP, GP LLC and the Subsidiaries, or any of their respective subsidiaries, is or may be subject, that, in the case of clauses (i), (ii) and (iii) above, is reasonably expected to (A) singly or in the aggregate have a material adverse effect on the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole, (B) prevent or result in the suspension of the offering and issuance of the Units or (C) in any manner draw into question the validity of this Agreement.

          (oo) No Subsidiary is currently prohibited, directly or indirectly, from paying any dividends to the Partnership, from making any other distribution on such Subsidiary’s capital stock or partnership or limited liability company 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 Pricing Disclosure Package and the Prospectus (exclusive of any amendment or supplement thereto).

          (pp) None of the Partnership, the General Partner, Plains AAP, GP LLC and the Subsidiaries has distributed and, prior to the later to occur of (i) any Delivery Date and (ii) completion of the distribution of the Firm Units or Option Units, as the case may be, will not distribute, any prospectus (as defined under the Securities Act) in connection with the offering and sale of the Units other than any Preliminary Prospectus, the Prospectus, any Issuer Free Writing Prospectus, subject to the conditions in Section 1(h) of this Agreement, or other materials, if any, permitted by the Securities Act, including Rule 134 of the Rules and Regulations.

          (qq) The Common Units are listed on the New York Stock Exchange (“ NYSE ”), and prior to the Initial Delivery Date, the Units will be approved for listing on the NYSE subject only to official notice of issuance.

          (rr) The Partnership 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 authorization; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets; (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 existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

          (ss) The Partnership and, to the knowledge of the Plains Parties, the directors and officers of GP LLC in their capacities as such, are in compliance in all material respects with all applicable and effective provisions of the Sarbanes-Oxley Act of 2002 and the rules and regulations promulgated thereunder.

          (tt) The Partnership maintains disclosure controls and procedures (as such term is defined in Rules 13a-15 and 15d-15 under the Exchange Act), that (i) are designed to provide reasonable assurance that material information relating to the Partnership, including its consolidated subsidiaries, is recorded, processed, summarized and communicated to the principal executive officer, the principal financial officer and other appropriate officers of GP LLC to allow for timely decisions regarding required disclosure, particularly during the periods in which the periodic reports required under the Exchange Act are being prepared; (ii) have been evaluated for effectiveness as of the end of the Partnership’s most recent fiscal quarter; and (iii) are effective in all material respects to perform the functions for which they are established.

          (uu) Based on the evaluation of its disclosure controls and procedures, the Partnership is not aware of (i) any significant deficiency or material weakness in the design or operation of internal controls over financial reporting that could adversely affect its ability to record, process, summarize and report financial data; or (ii) any fraud, whether or not material, that involves management or other employees who have a significant role in the internal controls over financial reporting of the Partnership.

          (vv) None of the Plains Entities nor, to the knowledge of the Plains Parties, any director, officer, agent, employee or affiliate of the Plains Entities 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 (the “ FCPA ”).

          (ww) No action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Plains Entities that involve allegations of money laundering is pending or, to the knowledge of the Plains Parties, threatened.

          (xx) None of the Plains Entities nor, to the knowledge of the Plains Parties, any director, officer or employee of the Plains Entities has received notice that it is subject to any sanctions administered by the Office of Foreign Assets Control of the U.S. Treasury Department (“ OFAC ”).

          2. Purchase and Sale . (a) Subject to the terms and conditions and in reliance upon the representations and warranties herein set forth, the Partnership agrees to sell to each Underwriter, and each Underwriter agrees, severally and not jointly, to purchase from the Partnership, at a purchase price of $44.78 per Unit, the amount of the Firm Units set forth opposite such Underwriter’s name in Schedule I hereto, subject to adjustment as set forth in Section 9 hereof.

          (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 900,000 Option Units at the same purchase price per Unit as the Underwriters shall pay for the Firm Units. Said option may be exercised in whole or in part at any time and from time to time on or before the 30th day after the date of the Prospectus upon written or telegraphic notice by Wachovia Capital Markets, LLC 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 (i) such adjustments as you in your absolute discretion shall make to eliminate any fractional shares and (ii) adjustment as set forth in Section 9 hereof.

          3. Delivery and Payment . Delivery of and payment for the Firm Units and the Option Units (if the option provided for in Section 2(b) hereof shall have been exercised on or before the third business day prior to the Initial Delivery Date) shall be made at the office of Vinson & Elkins L.L.P., 1001 Fannin, Houston, Texas 77002 at 9:00 a.m., Houston time, on May 12, 2008, 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 “ Initial Delivery Date ”). Delivery of the Units shall be made to the Underwriters for the respective accounts of the several Underwriters against payment by the several Underwriters of the purchase price thereof to or upon the order of the Partnership by wire transfer payable in same-day funds to an account specified by the Partnership. Delivery of the Firm Units and the Option Units shall be made through the facilities of The Depository Trust Company unless Wachovia Capital Markets, LLC shall otherwise instruct.

          If the option provided for in Section 2(b) hereof is exercised after the third business day prior to the Initial Delivery Date, the Partnership will deliver the Option Units (at the expense of the Partnership) to Wachovia Capital Markets, LLC, 375 Park Avenue, New York, New York 10152, Attention: Equity Syndicate Department, on the date (an “ Option Units Delivery Date ”) specified by the Underwriters (which shall be within three business days after each exercise of said option), for the respective accounts of the several Underwriters, against payment by the several Underwriters of the purchase price thereof to or upon the order of the Partnership by wire transfer payable in same-day funds to an account specified by the Partnership. If settlement for the Option Units occurs after the Initial Delivery Date, the Partnership will deliver to the Underwriters on the Option Units Delivery Date for the Option Units, and the obligation of the Underwriters to purchase the Option Units shall be conditioned upon receipt of, supplemental opinions, certificates and letters confirming as of such date the opinions, certificates and letters delivered on the Initial Delivery Date pursuant to Section 7 hereof. The Initial Delivery Date and any Option Units Delivery Date are each sometimes referred to as a “ Delivery Date .”

          4. Offering by Underwriters . It is understood that the several Underwriters propose to offer the Units for sale to the public as set forth in the Prospectus.

          5. Agreements of the Plains Parties . Each of the Plains Parties, jointly and severally, acknowledges and agrees with the Underwriters as follows:

          (a) If, at the Applicable Time, it is necessary for a post-effective amendment to the Registration Statement to be declared effective before the offering of the Units may commence, the Partnership, the General Partner, Plains AAP and GP LLC will endeavor to cause such post-effective amendment to become effective as soon as possible and will advise you promptly and, if requested by you, will confirm such advice in writing when such post-effective amendment has become effective.

          (b) The Partnership will advise you promptly and, if requested by you, will confirm such advice in writing: (i) of any request by the Commission for amendment of or a supplement to the Registration Statement, the Preliminary Prospectus or the Prospectus or for additional information; (ii) of the issuance by the Commission of any stop order suspending the effectiveness of the Registration Statement or of the suspension of qualification of the Units for offering or sale in any jurisdiction or the initiation of any proceeding for such purpose; and (iii) within the period of time referred to in paragraph (e) below, of any change in the condition (financial or other), business, prospects, properties, net worth or results of operations of the Plains Entities, taken as a whole, or of the happening of any event that makes any statement of a material fact made in the Registration Statement, the Pricing Disclosure Package or the Prospectus (as then amended or supplemented) untrue or that requires the making of any additions to or changes in the Registration Statement, the Pricing Disclosure Package or the Prospectus (as then amended or supplemented) in order to state a material fact required by the Securities Act or the regulations thereunder to be stated therein or necessary in order to make the statements therein (in the case of any Preliminary Prospectus or the Prospectus, in the light of the circumstances under which any such statements were made) not misleading, or of the necessity to amend or supplement the Prospectus (as then amended or supplemented) to comply with the Securities Act or any other applicable law. If at any time the Commission shall issue any stop order suspending the effectiveness of the Registration Statement, the Partnership, the General

Partner, Plains AAP and GP LLC will make every commercially reasonable effort to obtain the withdrawal of such order at the earliest possible time.

          (c) The Partnership will furnish to you, without charge, (i) one copy of the manually signed copy of the registration statement corresponding to the Commission’s electronic data gathering, analysis and retrieval system (“ EDGAR ”) version filed with the Commission and of each amendment thereto, including financial statements and all exhibits to the registration statement, (ii) such number of conformed copies of the registration statement as originally filed and of each amendment thereto, but without exhibits, as you or your counsel may reasonably request, (iii) such number of copies of the Incorporated Documents, without exhibits, as you may request, and (iv) such number of copies of the exhibits to the Incorporated Documents as you may request.

          (d) For such period as in the opinion of counsel for the Underwriters a prospectus is required by the Securities Act to be delivered in con