Adventure Exploration was a private exploration and production company based in Midland, Texas that focused on acquiring and exploiting properties in West Texas and Southeast New Mexico.

Bargo Energy was an exploration and production company based in Houston, Texas that focused on the acquisition, divestiture, development and production of oil and gas properties in Texas, Louisiana, California and New Mexico.

Blacksand Energy was a private exploration and production company based in Denver, Colorado that focused on production and development of primarily oil reserves in California.

Canaan Natural Gas was a private exploration and production company based in Oklahoma City, Oklahoma that focused on acquiring and exploiting long-lived natural gas reserves in the Anadarko and Arkoma Basins of Oklahoma and Arkansas.

Cannon Energy was a private exploration and production company based in Tulsa, Oklahoma that focused on developing coalbed methane assets in the Piceance and Appalachian Basins.

Cavallo Energy was a private exploration and production company based in Houston, Texas that focused on the acquisition and development of oil and gas properties in the Texas Panhandle.

Clipper Energy was a private exploration and production company based in Dallas, Texas that focused on the development of assets located in the Central Kansas Uplift area of Central Kansas.

Core Energy Holdings was a private exploration and production company based in Traverse City, Michigan that focused on CO₂ enhanced oil recovery projects in Northern Michigan.

Crestwood Midstream was a private midstream company based in Houston, Texas that focused on the acquisition and development of North American midstream assets.

Crusader Energy, Crusader Energy II and Crusader Energy III were private exploration and production companies based in Oklahoma City, Oklahoma that focused on acquiring and exploiting oil and gas properties in Oklahoma and the Texas Panhandle.

Energy Contractors is a private oilfield services company based in West Virginia and focused on the Appalachian Basin market. Energy Contractors' main service lines are rig mobilization, fluid management, frac tank rental, excavation services and well servicing.

Ensign Oil & Gas was a private exploration and production company based in Denver, Colorado that focused on the acquisition, development and exploitation of oil and gas properties in the Rocky Mountain and Mid-Continent regions.

The Exploration Company is a publicly traded exploration and production company based in San Antonio, Texas that focuses on the development of oil and gas properties in the Maverick Basin of South Texas.

Highland Oil & Gas was a private exploration and production company with offices in Houston, Tulsa and Fort Smith that focused on the development of conventional oil and gas properties in the Arkoma and Anadarko Basins of Arkansas and Oklahoma.

KA Compass was a private exploration and production company based in Houston, Texas that focused on the development of oil and gas properties in the Austin Chalk play in Texas.

Lyco Energy was a private exploration and production company based in Dallas, Texas that focused on the development and exploitation of primarily oil properties in Montana.

MarkWest Energy is a publicly traded master limited partnership headquartered in Denver, Colorado that engages in the gathering, transportation and processing of natural gas; the transportation, fractionation and storage of NGLs; and the gathering and transportation of crude oil. It conducts its operations in the Southwest, Northeast and Gulf Coast regions of the United States.

Medicine Bow Energy was a private exploration and production company based in Denver, Colorado that focused on the acquisition and exploitation of oil and gas properties in the Rocky Mountain region and East Texas.

Meridian Resource Corporation is a publicly traded exploration and production company based in Houston, Texas that focuses on the exploration and development of oil and gas reserves in Louisiana, Texas and the Gulf of Mexico.

OBENCO II was a private exploration and production company based in Shreveport, Louisiana that focused on the acquisition and development of oil and gas properties primarily in East Texas and other areas.

Plains All American Pipeline is a publicly traded master limited partnership headquartered in Houston, Texas that engages in the transportation, storage, terminalling and marketing of crude oil, refined products and liquefied petroleum gas and other natural gas related petroleum products.

Plains Resources was a publicly traded energy company based in Houston, Texas that focused on acquiring, exploiting and developing primarily oil properties in California.

Profico Energy was an exploration and production company based in Calgary, Alberta that focused on the development of primarily gas properties in Saskatchewan.

Quintana Minerals was a private exploration and production company based in Houston, Texas that focused on aggregating and exploiting oil and gas properties in Canada.

Sagebrush Resources was a private exploration and production company based in Denver, Colorado that focused on the acquisition and development of oil and gas properties in the Rocky Mountain region.

Sentra Resources Corporation was a private exploration and production company based in Calgary, Alberta that focused on exploring, acquiring and exploiting oil and gas assets in the Western Canadian Sedimentary Basin.

Stylus Exploration was a private exploration and production company based in Calgary, Alberta that focused on the development of oil and gas properties in Northeastern Alberta.

Trail Ridge Energy Partners was a private exploration and production company based in Dallas/Fort Worth, Texas that focused on the acquisition and development of oil and gas properties in Oklahoma and the Texas Panhandle.

Winter Ridge Energy was a private exploration and production company based in Denver, Colorado that focused on the acquisition and development of oil and gas properties in the Rocky Mountain region.