| 1 | O G & E | Oklahoma City, OK 73124 | Oil & Gas Operator | Feb 2014 |
| 2 | O K Swabbing Inc | Hennessey, OK 73742 | Oil & Gas Operator | Jan 2025 |
| 3 | O'Brien Energy Resources Corp | Portsmouth, NH 03801 | Oil & Gas Operator | Apr 2025 |
| 4 | O'Neill Properties, LTD. | Midland, TX 79702 | Oil & Gas Operator | Apr 2025 |
| 5 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 6 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Apr 2025 |
| 7 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jan 2025 |
| 8 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Jan 2025 |
| 9 | Oklahoma Oil Tactics Inc | Edmond, OK 73003-1351 | Oil & Gas Operator | Mar 2015 |
| 10 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Feb 2025 |
| 11 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 12 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 13 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 14 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Feb 2025 |
| 15 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Feb 2025 |
| 16 | Oryx Crude Trading & Transporation LP | Dallas, TX 75221 | Oil & Gas Operator | Jun 1999 |
| 17 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 18 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Feb 2025 |
| 19 | Oxley Petroleum Co | Oklahoma City, OK 73118-1044 | Oil & Gas Operator | Sep 2017 |
| 20 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Apr 2025 |