Anadarko Petroleum 10-Q 2009 Q3 Quarterly report

Exhibit 18

November 2, 2009

Anadarko Petroleum Corporation

Houston, Texas

Ladies and Gentlemen:

We have been furnished with a copy of the quarterly report on Form 10-Q of Anadarko Petroleum Corporation (the Company) for the three months ended September 30, 2009, and have read the Company’s statements contained in note 1 to the consolidated financial statements included therein. As stated in note 1, the Company changed its annual goodwill impairment testing date from January 1 to October 1. The Company states that the accounting change is preferable in the circumstances because the change ensures the completion of its annual goodwill impairment test prior to the end of its annual reporting period, thereby aligning impairment testing procedures with its year-end financial reporting. In accordance with your request, we have reviewed and discussed with Company officials the circumstances and business judgment and planning upon which the decision to make this change in the method of accounting was based.

We have not audited any financial statements of the Company as of any date or for any period subsequent to December 31, 2008, nor have we audited the information set forth in the aforementioned note 1 to the consolidated financial statements; accordingly, we do not express an opinion concerning the factual information contained therein.

With regard to the aforementioned accounting change, authoritative criteria have not been established for evaluating the preferability of one acceptable method of accounting over another acceptable method. However, for purposes of the Company’s compliance with the requirements of the Securities and Exchange Commission, we are furnishing this letter.

Based on our review and discussion, with reliance on management’s business judgment and planning, we concur that the newly adopted method of accounting is preferable in the Company’s circumstances.

Very truly yours,

/s/ KPMG