| 1 | California Oil Co | | Oil & Gas Operator | Aug 1965 |
| 2 | Cannon | Grand Junction, CO 81502 | Oil Operator | Dec 2025 |
| 3 | Cap Energy LLC | Greeley, CO 80634 | Oil & Gas Operator | Aug 2019 |
| 4 | Carbon Energy Corporation (USA) | Denver, CO 80290 | Oil & Gas Operator | Jul 2004 |
| 5 | Carter Oil Co | | Oil & Gas Operator | Dec 2013 |
| 6 | Celsius Energy Company | Denver, CO 80202-1558 | Oil & Gas Operator | Mar 2000 |
| 7 | Chandler & Associated Inc | Denver, CO 80202 | Oil & Gas Operator | Dec 1999 |
| 8 | Chevron Oil Company | | Oil & Gas Operator | Dec 1983 |
| 9 | Chevron USA Inc | Midland, TX 79706 | Oil & Gas Operator | Feb 2026 |
| 10 | Chorney Oil Co | Denver, CO 80203 | Oil & Gas Operator | Mar 1975 |
| 11 | Cig Exploration Inc | Houston, TX 77046 | Oil & Gas Operator | Nov 1999 |
| 12 | Cimarex Energy Co | Midland, TX 79706 | Oil & Gas Operator | Feb 2026 |
| 13 | Citation Oil & Gas Corp | Houston, TX 77269 | Oil & Gas Operator | Feb 2026 |
| 14 | Clinton Oil Company | Wichita, KS 67202 | Oil & Gas Operator | Apr 1980 |
| 15 | CNG Producing | New Orleans, LA 70112-6000 | Oil & Gas Operator | Jun 2000 |
| 16 | Coastal Oil & Gas Corp | Houston, TX 77252 | Oil & Gas Operator | Dec 2009 |
| 17 | Cobra Oil & Gas Corporation | Wichita Falls, TX 76307 | Oil & Gas Operator | Feb 2026 |
| 18 | Cochrane Resources Inc | Roosevelt, UT 84066 | Oil & Gas Operator | Jan 2026 |
| 19 | Colt Resources Corporation | Billings, MT 59103 | Oil & Gas Operator | Feb 2013 |
| 20 | Columbia Gas Development | Houston, TX 77251 | Oil & Gas Operator | Jun 1996 |
| 21 | Comanche Oil & Gas Corp | Salt Lake City, UT 84107-3075 | Oil & Gas Operator | May 2005 |
| 22 | Conley P Smith Operating | Denver, CO 80202 | Gas Operator | Dec 1983 |
| 23 | Conoco Inc | Houston, TX 77252 | Oil & Gas Operator | Mar 2015 |
| 24 | ConocoPhillips Company | Midland, TX 79701 | Oil & Gas Operator | Feb 2026 |
| 25 | Consolidated Oil & Gas Inc | Wichita, KS 67202 | Oil & Gas Operator | Dec 2012 |
| 26 | Continental Oil Co. | Durango, CO 81301 | Oil & Gas Operator | Dec 1983 |
| 27 | Coors Energy | Golden, CO 80402-0467 | Oil & Gas Operator | Sep 1992 |
| 28 | Coseka Resources USA LTD | Denver, CO 80202-1602 | Oil & Gas Operator | Jun 1988 |
| 29 | Costilla Energy, Inc. | Midland, TX 79702 | Oil & Gas Operator | Mar 2008 |
| 30 | Costilla Petroleum Corporation | Midland, TX 79702 | Oil & Gas Operator | Mar 2015 |
| 31 | Cotton Petroleum Corp/Apc | Denver, CO 80203-4549 | Oil & Gas Operator | Nov 1990 |
| 32 | Crain & Griffith DRL Co | | Oil Operator | Jun 1963 |
| 33 | Crescent Energy Operating, LLC | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 34 | Crescent Point Energy Us Corp | Denver, CO 80202 | Oil & Gas Operator | Apr 2024 |