| Company Name | Company Location | Company Type | Most Recent Production | |
|---|---|---|---|---|
| 1 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 2 | Union Exploration Partners, LTD. | Oil & Gas Operator | Aug 1990 | |
| 3 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 4 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 5 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 6 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Oct 2025 |
| 7 | United Gas Pipe Line Co. | Oil Operator | Aug 1993 | |
| 8 | United Operators, Inc. | Oil Operator | Sep 1999 | |
| 9 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 10 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Aug 2025 |