| 1 | Oakes Gas Co Inc | Kane, PA 16735-3905 | Gas Operator | Dec 2023 |
| 2 | Oakmont CC | Oakmont, PA 15139-1135 | Gas Operator | Dec 2024 |
| 3 | Ohio Kentucky Oil Corporation | Lexington, KY 40503 | Oil & Gas Operator | Dec 2023 |
| 4 | Oil & Gas MGMT Inc | Mount Pleasant, PA 15666-3304 | Oil & Gas Operator | Dec 2024 |
| 5 | Oil & Gas SVC Inc | Reelsville, IN 46171-9686 | Gas Operator | Dec 1991 |
| 6 | Oil Creek Operators LLC | Franklin, PA 16323 | Oil Operator | Dec 2025 |
| 7 | Old MTN Gas Co Inc | Pleasantville, PA 16341-0329 | Oil & Gas Operator | Dec 2020 |
| 8 | Olympus Energy, LLC | Canonsburg, PA 15317-7536 | Gas Operator | Jun 2025 |
| 9 | Olympus Prop Inc | Franklin Park, IL 60131-1418 | Oil & Gas Operator | Dec 1997 |
| 10 | Onexxx Prod & Exploration Corp | Jeannette, PA 15644-9691 | Gas Operator | Dec 2025 |
| 11 | Open Flow Gas Supply Corp | Du Bois, PA 15801-2442 | Oil & Gas Operator | Dec 2025 |
| 12 | Otter Exploration Inc | Warren, PA 16365-9689 | Oil & Gas Operator | Dec 2021 |
| 13 | Ows Acquisition Co LLC | Louisville, OH 44641 | Oil & Gas Operator | Dec 2024 |
| 14 | Ows Energy LLC | Carlton, PA 16311-1605 | Oil & Gas Operator | Dec 2025 |
| 15 | Oz Gas LTD | Tidioute, PA 16351-2648 | Oil & Gas Operator | Dec 2016 |