Anadarko Achieves Antitrust Clearance for Western Gas Resources Acquisition.

HOUSTON -- Anadarko Petroleum Corporation (NYSE:APC) today announced that its proposed acquisition of Western Gas Resources, Inc. (NYSE:WGR) has achieved U.S. antitrust clearance, as the statutory waiting period required under the Hart-Scott-Rodino Antitrust Improvements Act expired without issuance of a second request by the U.S. Federal Trade Commission.

Anadarko expects to close the transaction as soon as practicable following regulatory clearance from the Wyoming Public Service Commission and Western Gas shareholder approval at the special meeting set for Aug. 23.

ABOUT ANADARKO

Anadarko Petroleum Corporation's mission is to deliver a competitive and sustainable rate of return to shareholders by exploring for, acquiring and developing oil and natural gas resources vital to the world's health and welfare. As of year-end 2005, the company had 2.45 billion barrels-equivalent of proved reserves, making it one of the world's largest independent exploration and production companies. Anadarko's operational focus in North America extends from the deepwater Gulf of Mexico, up through the western U.S. and Canadian regions and onto the North Slope of Alaska. Anadarko's international activities are focused on major positions in North Africa, the Middle East and Indonesia, as well as exploration or production operations in several other countries. In June, Anadarko agreed to acquire Kerr-McGee Corporation (NYSE:KMG) and Western Gas Resources, Inc. (NYSE:WGR) in separate all-cash transactions totaling $21.1 billion, plus the assumption of debt estimated at $2.2 billion. For more information about how Anadarko is bringing excellence to the surface, please visit: www.anadarko.com.

This news release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Anadarko believes that its expectations are based on reasonable assumptions. No assurance, however, can be given that such expectations will prove to have been correct, or that the transactions described above will occur. A number of factors could cause actual results to differ materially from the projections, anticipated results or other expectations expressed in this news release. See "Risk Factors" in the company's 2005 Annual Report on Form 10-K and other public filings, press releases and discussions with company management. Anadarko undertakes no obligation to publicly update or revise any forward-looking statements.