| 1 | Oakland Petroleum Oper Co., Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Oct 2025 |
| 2 | Odessa Oil Investment Co., Inc. | Odessa, TX 79762 | Oil & Gas Operator | Nov 2016 |
| 3 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 4 | Oklahoma SWD Systems Inc | Odessa, TX 79762-8132 | Oil & Gas Operator | Jun 2025 |
| 5 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Jul 2025 |
| 6 | Old Dominion Oil Corporation | Oklahoma City, OK 73107 | Oil & Gas Operator | Apr 2009 |
| 7 | Ole Crow Operating | Wichita Falls, TX 76308 | Oil Operator | Jun 2025 |
| 8 | Oneok Gas Processing LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 9 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 10 | Oren Stone | Erick, OK 73645-4542 | Gas Operator | Jun 2022 |
| 11 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Jun 2025 |
| 12 | Oxley Petroleum Co | Oklahoma City, OK 73118-1044 | Oil & Gas Operator | Sep 2017 |
| 13 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |