| 1 | Uinta Oil & Gas | Roosevelt, UT 84066 | Oil & Gas Operator | Nov 1997 |
| 2 | Uinta Wax Operating, LLC | Fort Worth, TX 76107 | Oil & Gas Operator | May 2026 |
| 3 | Uintah Investors LLC | Vernal, UT 84078 | Oil & Gas Operator | May 2026 |
| 4 | Ultra Resources Inc | Houston, TX 77060 | Oil & Gas Operator | Sep 2018 |
| 5 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 6 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 7 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 8 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 9 | Union Petrochemical | | Oil & Gas Operator | Dec 1982 |
| 10 | Union Texas Petroleum | Houston, TX 77252 | Oil & Gas Operator | Oct 1991 |
| 11 | United Energy Corporation | San Antonio, TX 78209 | Oil & Gas Operator | Jul 2026 |
| 12 | United Producing Co Inc | | Oil & Gas Operator | May 1961 |
| 13 | United Utilities Corporation | Conroe, TX 77301 | Oil & Gas Operator | Oct 1998 |
| 14 | Universal Resources Corp. | Salt Lake Cty, UT 84145 | Oil & Gas Operator | Jan 2000 |
| 15 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Jul 2026 |
| 16 | Urban, C A & Tersell L W | | Gas Operator | Aug 1937 |
| 17 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | May 2026 |
| 18 | Utah Gas Op LTD | Rangely, CO 81648 | Oil & Gas Operator | Apr 2026 |
| 19 | Utah-Westar DRL Ventures | Dallas, TX 75201 | Oil & Gas Operator | Nov 1987 |
| 20 | Ute Energy Upstream Holdings LLC | Denver, CO 80202 | Oil & Gas Operator | Dec 2012 |
| 21 | Utex Oil Company | Elko, NV 89803 | Oil & Gas Operator | Dec 1988 |