X0202 4 2006-08-23 1 0000856716 WESTERN GAS RESOURCES INC WGR 0001228362 STONEHOCKER WALTER L 1099 18TH STREET, SUITE 1200 DENVER CO 80202 1 0 0 0 Common Stock 2006-08-23 4 D 0 3884506 61.00 D 0 D Stock Option (Right to Buy) 18.91 2006-08-23 4 D 0 4000 0 D 2003-05-17 2008-05-17 Common Stock 4000 0 D Stock Option (Right to Buy) 19.38 2006-08-23 4 D 0 4000 0 D 2004-05-19 2009-05-19 Common Stock 4000 0 D Stock Option (Right to Buy) 27.685 2006-08-23 4 D 0 4000 0 D 2005-05-10 2010-05-10 Common Stock 4000 0 D Stock Option (Right to Buy) 34.00 2006-08-23 4 D 0 4000 0 D 2006-05-06 2011-05-06 Common Stock 4000 0 D Stock Option (Right to Buy) 52.78 2006-08-23 4 D 0 4000 0 D 2007-05-05 2012-05-05 Common Stock 4000 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 Walter L. Stonehocker 2006-08-23