| 1 | U S Liquids Of La., L.P. | | Oil Operator | Apr 2014 |
| 2 | U. D. Man, Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Oct 2025 |
| 3 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 4 | Ultramar Production Company | | Oil & Gas Operator | Dec 1991 |
| 5 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 6 | Union Exploration Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 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 | Sep 2002 |
| 9 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 10 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 11 | United Operators, Inc. | | Oil Operator | Sep 1999 |
| 12 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 13 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Oct 2025 |
| 14 | Us Liquids Of La, LTD | | Oil Operator | Jul 2002 |
| 15 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Aug 2025 |