| 1 | O'Brien Energy Resources Corp | Portsmouth, NH 03801 | Oil & Gas Operator | Oct 2025 |
| 2 | Ocean Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 3 | Oci LLC | Thermopolis, WY 82443 | Oil Operator | Jan 2024 |
| 4 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Jun 2025 |
| 5 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | Sep 2025 |
| 6 | Oil & Gas Acquisition Group Inc | Austin, TX 78716 | Oil & Gas Operator | May 2003 |
| 7 | Oil Mountain Energy Inc | Casper, WY 82609 | Oil Operator | Aug 2025 |
| 8 | Oildigger Resources Fund L LLLP | Billings, MT 59101 | Oil & Gas Operator | Aug 2025 |
| 9 | Oilfield Consultants | | Oil & Gas Operator | Dec 1987 |
| 10 | Oilfield Salvage & Service Company | Littleton, CO 80120 | Oil & Gas Operator | Aug 2025 |
| 11 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 12 | Oklahoma Oil Company | Dallas, TX 75206 | Oil & Gas Operator | Aug 2013 |
| 13 | Okmar Oil Company | Marietta, OH 45750 | Oil & Gas Operator | Jun 2005 |
| 14 | Okt Petroleum Company Inc | Oklahoma City, OK 73118-7425 | Oil & Gas Operator | Oct 2013 |
| 15 | Olds Oil Company | Casper, WY 82604 | Oil Operator | Jun 1988 |
| 16 | Olympic Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Jul 2004 |
| 17 | Omimex Petroleum Inc (Co) | Newcastle, WY 82701 | Oil & Gas Operator | May 2001 |
| 18 | Omimex Petroleum Inc (De) | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2020 |
| 19 | Omni Operating Company | Osage, WY 82723 | Oil & Gas Operator | Sep 2001 |
| 20 | Oneida Energy Corporation | Tulsa, OK 74137 | Oil & Gas Operator | Jul 2003 |
| 21 | Open Range Energy LLC | Jones, OK 73049-8744 | Oil & Gas Operator | Mar 2025 |
| 22 | Opes Production Inc | Buffalo, WY 82834 | Gas Operator | Mar 2015 |
| 23 | Orion Energy Partners LP | Denver, CO 80202 | Oil & Gas Operator | Nov 2010 |
| 24 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 25 | Osage Hot Oil Service | Newcastle, WY 82701 | Oil & Gas Operator | Jul 1997 |
| 26 | Osage Operating Company LLC | Seattle, WA 98133 | Oil Operator | May 2006 |
| 27 | Osage Partners LLC | | Oil & Gas Operator | Aug 2025 |
| 28 | Osborn Heirs Company LTD | San Antonio, TX 78217 | Oil & Gas Operator | Jun 2025 |
| 29 | Ott Inc | Casper, WY 82602 | Oil Operator | Jul 2025 |
| 30 | Overland Resources LLC | Greenwood VIllage, CO 80111 | Oil & Gas Operator | Jul 2019 |
| 31 | Ovintiv USA Inc. | Denver, CO 80202 | Oil & Gas Operator | Oct 2025 |
| 32 | Oxbow Properties Inc | Centennial, CO 80122-1422 | Oil & Gas Operator | Jan 2025 |
| 33 | Oxford Exploration Company | Denver, CO 80237 | Oil & Gas Operator | Aug 1995 |
| 34 | Oxtex Inc | | Oil & Gas Operator | Oct 1989 |
| 35 | Oxy Petroleum Inc | | Oil & Gas Operator | Jan 1986 |
| 36 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |