| 1 | O'Blue Corp. | Kerrville, TX 78028 | Oil & Gas Operator | Mar 1998 |
| 2 | O'Hern Morris D | Mounds, OK 74047-5163 | Oil & Gas Operator | Sep 2016 |
| 3 | O'Neal Oil & Gas Co | Fort Worth, TX 76107-1479 | Oil & Gas Operator | Feb 2026 |
| 4 | Octagon Resources LLC | Norman, OK 73071-1295 | Oil & Gas Operator | May 2015 |
| 5 | Odell Larry | Oologah, OK 74053 | Oil Operator | Apr 2011 |
| 6 | Oil Property Management Inc | Attica, KS 67009 | Oil & Gas Operator | Feb 2021 |
| 7 | Oil Recovery Systems Inc | Tulsa, OK 74145-4619 | Oil & Gas Operator | Jan 2026 |
| 8 | Oklahoma Liquid Resources Inc | Collinsville, OK 74021 | Oil & Gas Operator | Dec 2025 |
| 9 | Oklahoma O & G Royalties Inc | Duncan, OK 73533 | Oil & Gas Operator | Nov 2000 |
| 10 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Jan 2026 |
| 11 | Oklahoma Oil And Gas Resources LLC | Guthrie, OK 73044-8095 | Oil & Gas Operator | Jan 2026 |
| 12 | Oklahoma Prod & Exp Co | Broken Arrow, OK 74012 | Oil & Gas Operator | May 2013 |
| 13 | Oklaoleum Oil And Gas Inc | Bristow, OK 74010-0057 | Oil Operator | Jan 2016 |
| 14 | Okmar Oil Company | Marietta, OH 45750 | Oil & Gas Operator | Jun 2005 |
| 15 | Okt Petroleum Company Inc | Oklahoma City, OK 73118-7425 | Oil & Gas Operator | Oct 2013 |
| 16 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 17 | Omega Energy, LLC | Corpus Christ, TX 78418 | Oil & Gas Operator | Apr 2026 |
| 18 | Omimex International Corp | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Jan 2026 |
| 19 | Onapa Gas Company LLC | Tulsa, OK 74136-7253 | Gas Operator | Nov 2019 |
| 20 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |
| 21 | Open Door Holdings Inc | Surprise, AZ 85387-2015 | Oil & Gas Operator | Feb 2024 |
| 22 | Open Door Productions Inc | Muskogee, OK 74401-1032 | Oil & Gas Operator | Apr 2020 |
| 23 | Oso Resources LLC | Edmond, OK 73003 | Oil & Gas Operator | Jan 2026 |
| 24 | Overland Investments Inc | Coweta, OK 74429 | Oil & Gas Operator | Jan 2026 |
| 25 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Feb 2026 |