See Instrument Society Of America

Incorporated in July 1999 and changed name to Nido Petroleum Limited

Patterson-UTI Energy subsidiary owns onshore exploration and production royalty interests; operations were transferred to CML Exploration LLC in November 2007.

Merged with Windsor Energy in 1997 to form Pegasi Energy Resource Corporation

Merged with SMK Energy Corporation in 1997 to form Pegasi Energy Resource Corporation

Sold to C&T Enterprises in 2002. Name changed to Valley Energy

ARCO purchased Thrifty Oil and its 260 retail stations in March 1997

ARCO purchased parent Thrifty Oil and its 260 retail stations in March 1997

Acquired by Provident Energy Trust in 2004

Acquired by Vermilion Resources Ltd in March 2002. See Vermilion Energy Trust

Changed name to Republic Resources LLC in 1997

Acquired by Southern Union Company in March 2006 and name changed to Southern Union Gas Services

Acquired by Anadarko Petroleum Corp in January 2001

Lyondell Chemical Co acquired CITGO's 41.25% ownership interest in Lyondell-Citgo Refining LP in August 2006, see Houston Refining LP

Merged with Chesapeake Energy Corporation in 2001

acquired by Patrick Petroleum Company in November 1999

Acquired by UMC Petroleum Corporation in August 1990. See United Meridian Corporation

Acquired by ERC Industries Inc in December 1986. Exploration and production properties subsequently sold off to foreign interest groups.

Acquired by Probe Exploration Inc

Put into receivership in March 2000

Acquired by KCS Energy in 1997

Acquired by Amax Oil & Gas Corporation in 1990

Acquired by Traver Oil Company

Acquired by Earlsboro Energies Corporation