| 1 | O'Neal Oil & Gas Co | Fort Worth, TX 76107-1479 | Oil & Gas Operator | Apr 2025 |
| 2 | O'Neal Oil Company | Nocona, TX 76255 | Oil & Gas Operator | Jun 2025 |
| 3 | O'Neal, Lindell | Nocona, TX 76255 | Oil & Gas Operator | Mar 2025 |
| 4 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Jun 2025 |
| 5 | Oilbank Production LLC | Norman, OK 73072 | Oil Operator | Mar 2025 |
| 6 | Oilco Energy Inc | Duncan, OK 73533 | Oil & Gas Operator | Mar 2015 |
| 7 | Oilwell Operators, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Jun 2025 |
| 8 | Oklahoma O & G Royalties Inc | Duncan, OK 73533 | Oil & Gas Operator | Nov 2000 |
| 9 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Mar 2025 |
| 10 | Oklahoma Prime Energy LLC | Ardmore, OK 73401 | Oil Operator | May 2020 |
| 11 | Oklahoma Tank Service Inc | Oklahoma City, OK 73143 | Oil Operator | Aug 1997 |
| 12 | Okmar Oil Company | Marietta, OH 45750 | Oil & Gas Operator | Jun 2005 |
| 13 | Oktex Operating LLC | Edmond, OK 73013-1961 | Oil & Gas Operator | May 2020 |
| 14 | Old Dominion Oil Corporation | Oklahoma City, OK 73107 | Oil & Gas Operator | Apr 2009 |
| 15 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 16 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 17 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |
| 18 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 19 | Otc/Occ Not Assigned | | Oil & Gas Operator | Dec 2024 |
| 20 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Apr 2025 |
| 21 | Ovintiv USA Inc. | Denver, CO 80202 | Oil & Gas Operator | Jun 2025 |
| 22 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Jun 2025 |