| 1 | Oasis Energy Resources LLC | Norman, OK 73072-9668 | Oil & Gas Operator | Jun 2025 |
| 2 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 3 | Oklahoma Energy Acquisitions LP | Houston, TX 77094-1900 | Oil & Gas Operator | Jul 2025 |
| 4 | Oklahoma Equipment & Salvage | Oklahoma City, OK 73120-5903 | Oil & Gas Operator | Mar 2015 |
| 5 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Jun 2025 |
| 6 | Oklahoma Oil Tactics Inc | Edmond, OK 73003-1351 | Oil & Gas Operator | Mar 2015 |
| 7 | Oklahoma Tank Service Inc | Oklahoma City, OK 73143 | Oil Operator | Aug 1997 |
| 8 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Jul 2025 |
| 9 | Omni Oil & Gas, Inc. | San Antonio, TX 78229 | Oil & Gas Operator | Oct 2017 |
| 10 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |
| 11 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 12 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Jul 2025 |
| 13 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 14 | Optima Exploration LLC | Tulsa, OK 74116-5664 | Oil & Gas Operator | Mar 2015 |
| 15 | Oshtah Oil Company LLC | Stratford, OK 74872 | Oil & Gas Operator | Sep 2018 |
| 16 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 17 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Jun 2025 |
| 18 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |