| 1 | U.S. Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 2 | Ultra Oil & Gas, Inc. | Centerton, AR 72719 | Oil & Gas Operator | May 2024 |
| 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 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | May 2024 |
| 6 | United Oil & Minerals L. P. | Austin, TX 78746 | Oil & Gas Operator | Jun 2003 |
| 7 | United Oil & Minerals, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jan 2001 |
| 8 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 9 | United Texas Petroleum Inc. | McKinney, TX 75070 | Oil & Gas Operator | May 2024 |
| 10 | Universal Resources Corp. | Salt Lake Cty, UT 84145 | Oil & Gas Operator | Jan 2000 |
| 11 | Unoso Operating Company L.L.C. | Georgetown, TX 78633 | Oil & Gas Operator | May 2024 |
| 12 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | May 2024 |