| 1 | O G & E | Oklahoma City, OK 73124-0300 | Oil & Gas Operator | Feb 2014 |
| 2 | O'Neal Oil & Gas Co | Fort Worth, TX 76107-1479 | Oil & Gas Operator | Feb 2024 |
| 3 | Obele Operating Company LLC | Sedona, AZ 86336-5745 | Oil & Gas Operator | Jan 2024 |
| 4 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 5 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Apr 2024 |
| 6 | Oil Recovery Systems Inc | | Oil & Gas Operator | Jan 2024 |
| 7 | Oilfield Operating Company | Cushing, OK 74023-1347 | Oil & Gas Operator | Jan 2018 |
| 8 | Oklahoma & Northwestern Co. | Oklahoma City, OK 73102 | Oil & Gas Operator | Jan 1997 |
| 9 | Oklahoma Equipment & Salvage | Oklahoma City, OK 73120-5903 | Oil & Gas Operator | Mar 2015 |
| 10 | Oklahoma Liquid Resources Inc | Owasso, OK 74055-0841 | Oil & Gas Operator | Jan 2024 |
| 11 | Oklahoma Oil & Gas MGMT Inc | | Oil & Gas Operator | Jan 2024 |
| 12 | Oklahoma Petroleum Allies LLC | Ardmore, OK 73401 | Oil Operator | Oct 2023 |
| 13 | Oklahoma Prime Energy LLC | | Oil Operator | May 2020 |
| 14 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Feb 2024 |
| 15 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 16 | Oneok Gas Processing LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 17 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 18 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 19 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 20 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Feb 2024 |
| 21 | Oryx Crude Trading & Transporation LP | Dallas, TX 75221 | Oil & Gas Operator | Jun 1999 |
| 22 | Osborn Heirs Co | San Antonio, TX 78217 | Oil & Gas Operator | Mar 2024 |
| 23 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Jan 2024 |
| 24 | Ovintiv USA Inc. | Denver, CO 80202 | Oil & Gas Operator | Apr 2024 |
| 25 | Oxley Petroleum | Tulsa, OK 74119-3609 | Oil & Gas Operator | Jan 2020 |
| 26 | Oxley Petroleum Co | Oklahoma City, OK 73118-1044 | Oil & Gas Operator | Sep 2017 |
| 27 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Apr 2024 |