| 1 | U V Industries | | Oil & Gas Operator | Jan 1993 |
| 2 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 3 | Underwood Oil & Gas | Casper, WY 82602 | Oil & Gas Operator | Mar 2024 |
| 4 | Unicorn Drilling Inc | Cody, WY 82414 | Oil Operator | Dec 1998 |
| 5 | Unioil | Denver, CO 80203 | Oil & Gas Operator | Jun 2012 |
| 6 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 7 | Union Texas Petroleum | Houston, TX 77252 | Oil & Gas Operator | Oct 1991 |
| 8 | Unit Drilling & Exploration Co | Tulsa, OK 74132-5300 | Oil & Gas Operator | Dec 2023 |
| 9 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | May 2024 |
| 10 | United Energy Corporation | San Antonio, TX 78209 | Oil & Gas Operator | May 2024 |
| 11 | United Natural Gas LLC | Denver, CO 80202 | Oil & Gas Operator | Feb 2020 |
| 12 | United Natural Resources Corp | | Oil Operator | Jan 1986 |
| 13 | United Petroleum Corporation | Edgwater, CO 80214 | Oil & Gas Operator | May 1996 |
| 14 | United Utilities Corp | Conroe, TX 77301 | Oil & Gas Operator | Oct 1998 |
| 15 | Universal Fuels Company | | Oil & Gas Operator | Oct 1993 |
| 16 | Updike Resources Inc | Newcastle, WY 82701 | Oil & Gas Operator | Jun 1998 |
| 17 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | May 2024 |
| 18 | Urroz Oil & Gas LLC | Evanston, WY 82931 | Oil & Gas Operator | Jun 2020 |
| 19 | Us Energy Corp. | Houston, TX 77057 | Oil & Gas Operator | Dec 2021 |
| 20 | Us Ore Corporation | Pacific Beach, CA 92109 | Oil Operator | Feb 2014 |
| 21 | USA Energy LLC | Lance Creek, WY 82222 | Oil & Gas Operator | Nov 2023 |
| 22 | USA Exploration & Production LLC | Mills, WY 82644 | Oil & Gas Operator | Sep 2012 |