Plains All American Pipeline (PAA) 10-Q 2004 Q2 Quarterly report

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Exhibit 18.1

August 6, 2004

Board of Directors
Plains All American GP LLC, the general partner of
Plains AAP, L.P., the general partner of
Plains All American Pipeline, L.P.
333 Clay Street, Suite 1600
Houston, Texas 77002-4101

Dear Directors:

        We are providing this letter to you for inclusion as an exhibit to Plains All American Pipeline, L.P.'s ("PAA") Form 10-Q filing pursuant to Item 601 of Regulation S-K.

        We have been provided a copy of PAA's Quarterly Report on Form 10-Q for the period ended June 30, 2004. Note 1 therein describes a change in accounting principle from recording pipeline linefill held in pipelines not owned by PAA ("linefill in third party assets") as a separate asset to including linefill in third party assets in operating inventory. It should be understood that the preferability of one acceptable method of accounting over another for linefill in third party assets has not been addressed in any authoritative accounting literature, and in expressing our concurrence below we have relied on management's determination that this change in accounting principle is preferable. Based on our reading of management's stated reasons and justification for this change in accounting principle in the Form 10-Q, and our discussions with management as to their judgment about the relevant business planning factors relating to the change, we concur with management that such change represents, in PAA's circumstances, the adoption of a preferable accounting principle in conformity with Accounting Principles Board Opinion No. 20.

        We have not audited any financial statements of PAA as of any date or for any period subsequent to December 31, 2003. Accordingly, our comments are subject to change upon completion of an audit of the consolidated financial statements covering the period of the accounting change.

Very truly yours,

PricewaterhouseCoopers LLP

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Exhibit 18.1