| 1 | O G & E | Oklahoma City, OK 73124 | Oil & Gas Operator | Feb 2014 |
| 2 | O K Swabbing Inc | Hennessey, OK 73742 | Oil & Gas Operator | Sep 2024 |
| 3 | Oklahoma Energy Acquisitions LP | Houston, TX 77094-1900 | Oil & Gas Operator | Sep 2024 |
| 4 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Oct 2024 |
| 5 | Oklahoma Oil Tactics Inc | Edmond, OK 73003-1351 | Oil & Gas Operator | Mar 2015 |
| 6 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Oct 2024 |
| 7 | Okmar Oil Company | Marietta, OH 45750 | Oil & Gas Operator | Jun 2005 |
| 8 | Okt Petroleum Company Inc | Oklahoma City, OK 73118-7425 | Oil & Gas Operator | Oct 2013 |
| 9 | Olympic Petroleum Company | Tulsa, OK 74114 | Oil & Gas Operator | Jun 1998 |
| 10 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 11 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 12 | Open Range Energy LLC | Jones, OK 73049-8744 | Oil & Gas Operator | Jul 2024 |
| 13 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Oct 2024 |
| 14 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 15 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Oct 2024 |