| 1 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 2 | Union Exploration Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 3 | Union Gas Operating Company | Houston, TX 77014 | Oil & Gas Operator | Oct 2025 |
| 4 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 5 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 6 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 7 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 8 | United Operators, Inc. | | Oil Operator | Sep 1999 |
| 9 | United Petroleum Corporation | Edgwater, CO 80214 | Oil & Gas Operator | May 1996 |
| 10 | Universal Drilling Co., Inc. | Denver, CO 80203 | Oil & Gas Operator | Sep 2003 |
| 11 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 12 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Oct 2025 |
| 13 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Aug 2025 |