X0202 4 2006-08-23 1 0000856716 WESTERN GAS RESOURCES INC WGR 0001354703 Gagnon Paul G 1099 18TH STREET DENVER CO 80202 0 1 0 0 VP WGR Canada Company Common Stock 2006-08-23 4 D 0 4594 61.00 D 0 D Stock Option (Right to Buy) 34.28 2006-08-23 4 D 0 26667 0 D 2006-03-01 2011-03-01 Common Stock 26667 0 D Stock Option (Right to Buy) 35.21 2006-08-23 4 D 0 3334 0 D 2006-03-30 2011-03-30 Common Stock 3334 0 D Stock Option (Right to Buy) 31.85 2006-08-23 4 D 0 5334 0 D 2006-05-19 2011-05-19 Common Stock 5334 0 D Stock Option (Right to Buy) 43.43 2006-08-23 4 D 0 12091 0 D 2007-02-24 2012-02-24 Common Stock 12091 0 D On August 23, 2006, at the effective time of the merger contemplated by the Agreement and Plan of Merger, dated as of June 22, 2006, among Anadarko Petroleum Corporation, APC Merger Sub, Inc. and Western Gas Resources, Inc., the shares of common stock listed in Table I were automatically cancelled and converted into the right to receive $61.00 in cash. On August 23, 2006, at the effective time of the merger contemplated by the Agreement and Plan of Merger, dated as of June 22, 2006, among Anadarko Petroleum Corporation, APC Merger Sub, Inc. and Western Gas Resources, Inc., each option became immediately and fully vested and was cancelled and converted into the right to receive a cash amount equal to the excess of $61.00 over the option exercise price multiplied by the number of shares subject to such option. The vesting of all options accelerates at the effective time of the merger contemplated by the Agreement and Plan of Merger, dated as of June 22, 2006, among Anadarko Petroleum Corporation, APC Merger Sub, Inc. and Western Gas Resources, Inc. /s/ John C. Walter, as Attorney-in-Fact for Paul G. Gagnon 2006-08-23