| Company Name | Company Location | Company Type | Most Recent Production | |
|---|---|---|---|---|
| 1 | O'Brien-Sill | Oil & Gas Operator | Sep 2025 | |
| 2 | Oakland Petroleum Oper Co., Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Dec 2025 |
| 3 | Occidental Of Elk Hills Inc. | Oil & Gas Operator | Dec 2014 | |
| 4 | Occidental Petroleum Corporation | Oil & Gas Operator | Dec 2021 | |
| 5 | Ogle Petroleum Inc. | Oil & Gas Operator | Dec 1989 | |
| 6 | Omimex Petroleum Inc | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2022 |
| 7 | Oro Negro Inc. | Oil & Gas Operator | Dec 2004 | |
| 8 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 9 | Oxy Petroleum Inc | Oil & Gas Operator | Jan 1986 | |
| 10 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Dec 2025 |