TABLE OF CONTENTS

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Exhibits

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MEMBERSHIP INTEREST PURCHASE AGREEMENT

THIS MEMBERSHIP INTEREST PURCHASE AGREEMENT, dated as of August 19, 2005 (this “Agreement”), is entered into by and between Sempra Energy Trading Corp., a Delaware corporation (“Seller”), and PAA/Vulcan Gas Storage, LLC, a Delaware limited liability company (“Buyer”).

RECITALS

WHEREAS, Seller owns one hundred percent (100%) of the issued and outstanding capital stock of the Company;

WHEREAS, the Company owns one hundred percent (100%) of the issued and outstanding capital stock of each of BGS Corp. and PPEC Corp.;

WHEREAS, BGS Corp. owns one hundred percent (100%) of the membership interests in Bluewater Gas Storage, LLC, a Delaware limited liability company (“BGS LLC”), and PPEC Corp. owns one hundred percent (100%) of the membership interests in Pine Prairie Energy Center, LLC, a Delaware limited liability company (“PPEC LLC”; and together with each of BGS Corp., PPEC Corp. and BGS LLC, a “Subsidiary” and, collectively, the “Subsidiaries”);

WHEREAS, BGS LLC owns and operates a natural gas storage facility located in Macombe and St. Clair Counties, Michigan, which facility includes certain buildings, equipment, compressors, structures, and pipelines located on a substantially depleted reservoir known as the Columbus III Reservoir (the “BGS Storage Facility”), and PPEC LLC is engaged in the development of a salt cavern natural gas storage facility located in Evangeline Parish, Louisiana (the “Project”); and

WHEREAS, Seller desires to sell to Buyer, and Buyer desires to purchase from Seller, all of the membership interests in the Company (the “Membership Interests”) which shall have been issued to Seller in exchange for, and upon the cancellation of, all of the issued and outstanding capital stock of the Company (the “Shares”) pursuant to the Conversion Transactions.

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:

“1935 Act” has the meaning provided such term in Section 4.21.

“Acquisition Agreements” means the agreements listed on Schedule 9.5.

“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.  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.