| 1 | O G & E | Oklahoma City, OK 73124 | Oil & Gas Operator | Feb 2014 |
| 2 | O K Swabbing Inc | Hennessey, OK 73742 | Oil & Gas Operator | Nov 2025 |
| 3 | O'Neill Properties, LTD. | Midland, TX 79702 | Oil & Gas Operator | Feb 2026 |
| 4 | Oak Valley SWD LLC | Enid, OK 73703-4637 | Oil Operator | Aug 2022 |
| 5 | Odessa Natural Corporation | | Oil & Gas Operator | Dec 1991 |
| 6 | Odessa Oil Investment Co., Inc. | Odessa, TX 79762 | Oil & Gas Operator | Nov 2016 |
| 7 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 8 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 9 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Feb 2026 |
| 10 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Nov 2025 |
| 11 | Oklahoma Energy Acquisitions LP | Houston, TX 77094-1900 | Oil & Gas Operator | Nov 2025 |
| 12 | Oklahoma Equipment & Salvage | Oklahoma City, OK 73120-5903 | Oil & Gas Operator | Mar 2015 |
| 13 | Oklahoma Natural Resources Inc | Woodward, OK 73801 | Oil & Gas Operator | Sep 1996 |
| 14 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Nov 2025 |
| 15 | Oklahoma Oil Tactics Inc | Edmond, OK 73003-1351 | Oil & Gas Operator | Mar 2015 |
| 16 | Oklahoma Plugging & Equip Inc | | Oil & Gas Operator | Nov 2000 |
| 17 | Oklahoma Rig & Salvage Inc | Oklahoma City, OK 73114 | Oil & Gas Operator | Mar 2015 |
| 18 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 19 | Omimex International Corp | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Nov 2025 |
| 20 | Omni Oil & Gas, Inc. | San Antonio, TX 78229 | Oil & Gas Operator | Oct 2017 |
| 21 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 22 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 23 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |
| 24 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 25 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 26 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 27 | Osage Oil & Transportation Inc | Cleveland, OK 74020 | Oil & Gas Operator | Nov 2000 |
| 28 | Osborn Heirs Co | San Antonio, TX 78217 | Oil & Gas Operator | Dec 2025 |
| 29 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 30 | Overflow Energy Stack LLC | Booker, TX 79005 | Oil Operator | Sep 2022 |
| 31 | Overflow Energy, LLC | Perryton, TX 79070 | Oil & Gas Operator | Feb 2026 |
| 32 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Dec 2025 |
| 33 | Ovintiv USA Inc. | Denver, CO 80202 | Oil & Gas Operator | Feb 2026 |
| 34 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Feb 2026 |