| 1 | Octagon Resources LLC | Norman, OK 73071-1295 | Oil & Gas Operator | May 2015 |
| 2 | Oil & Gas Exploration Inc | Cleveland, OK 74020 | Oil & Gas Operator | Aug 2013 |
| 3 | Oil State Petroleum Inc | Jennings, OK 74038 | Oil & Gas Operator | Jan 2024 |
| 4 | Oilfield Operating Company | Cushing, OK 74023-1347 | Oil & Gas Operator | Jan 2018 |
| 5 | Oilton Petroleum Inc | Oilton, OK 74052-0459 | Oil & Gas Operator | Oct 2001 |
| 6 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jan 2024 |
| 7 | Oklahoma Cellulose Inc | Cleveland, OK 74020-0193 | Oil Operator | Jan 2024 |
| 8 | Oklahoma Liquid Resources Inc | Owasso, OK 74055-0841 | Oil & Gas Operator | Jan 2024 |
| 9 | Oklahoma Oil & Gas MGMT Inc | | Oil & Gas Operator | Jan 2024 |
| 10 | Oklahoma Petroleum Allies LLC | Ardmore, OK 73401 | Oil Operator | Oct 2023 |
| 11 | Okt Petroleum Company Inc | Oklahoma City, OK 73118-7425 | Oil & Gas Operator | Oct 2013 |
| 12 | Osage Oil & Transportation Inc | Cleveland, OK 74020 | Oil & Gas Operator | Nov 2000 |
| 13 | Osburn Gerald Dba Ozzy & Son Oil & Gas | Drumright, OK 74030-5467 | Oil Operator | Oct 2020 |
| 14 | Osterhout Phillip L | Drumright, OK 74030-0693 | Oil & Gas Operator | Jan 2014 |
| 15 | Oxford Oil Inc | Cleveland, OK 74020 | Oil & Gas Operator | Feb 1997 |