| 1 | U-N-I Exploratio | | Oil & Gas Operator | Dec 1990 |
| 2 | U-N-I Exploration & Development, Inc. | Yates Center, KS 66783 | Oil & Gas Operator | Jan 2003 |
| 3 | Uehlin LLC | Oberlin, KS 67749 | Oil Operator | Dec 2024 |
| 4 | Uhls, Jimmie J. | Sedan, KS 67361 | Oil Operator | Sep 2019 |
| 5 | Ulysses, City Of | Ulysses, KS 67880 | Gas Operator | Jun 2025 |
| 6 | Ummel'S Tank Ser | | Oil Operator | Sep 1994 |
| 7 | Unc Texas Incorp | | Gas Operator | May 1987 |
| 8 | Union Pacific Re | | Oil & Gas Operator | Dec 1996 |
| 9 | Union Pacific Resour | | Oil & Gas Operator | Apr 2002 |
| 10 | Union Texas Petroleum | Houston, TX 77252 | Oil & Gas Operator | Oct 1991 |
| 11 | Union Valley Petroleum Corporation | Enid, OK 73701 | Oil & Gas Operator | Jul 2025 |
| 12 | Unionville Explo | | Oil Operator | Jul 1984 |
| 13 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Oct 2025 |
| 14 | United Energy & Exploration LLC | Ada, OK 74821 | Oil & Gas Operator | Jun 2025 |
| 15 | United Energy Inc. | Wichita, KS 67230 | Oil & Gas Operator | Dec 2002 |
| 16 | United Meridian | | Oil Operator | Dec 1992 |
| 17 | United Oil & Gas | | Oil Operator | Feb 1988 |
| 18 | United Petroleum | | Oil Operator | Mar 1986 |
| 19 | United Petroleum Corporation | Edgwater, CO 80214 | Oil & Gas Operator | May 1996 |
| 20 | United Reserve G | | Oil Operator | Aug 1987 |
| 21 | United States Exploration, Inc. | Denver, CO 80802 | Oil & Gas Operator | Jun 2009 |
| 22 | Universal Resour | | Oil & Gas Operator | Dec 1996 |
| 23 | Universal Resources Corp. | Salt Lake Cty, UT 84145 | Oil & Gas Operator | Jan 2000 |
| 24 | Unknown | Houston, TX 77208 | Oil & Gas Operator | Dec 2023 |
| 25 | Unrein Oil Co | | Oil Operator | Jun 2025 |
| 26 | Unruh, Elmer | Galva, KS 67443 | Oil & Gas Operator | Aug 1998 |
| 27 | Unruh, Mark D. | Peru, KS 67360 | Oil Operator | Sep 2011 |
| 28 | Upland Resources | | Oil Operator | Jul 1983 |
| 29 | Upland Resources, Inc. | Canadian, TX 79014 | Oil & Gas Operator | Dec 2009 |
| 30 | Uranus, Inc. | Kansas City, MO 64112 | Oil Operator | Jan 2000 |
| 31 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Oct 2025 |
| 32 | Us Energy Exploration Corp | Rural Valley, PA 16249 | Oil & Gas Operator | May 2025 |
| 33 | Us Oil Resources LLC | Lakewood, CO 80123 | Oil Operator | Jun 2025 |
| 34 | Usins Oil Compan | | Oil Operator | Jan 1993 |
| 35 | Usx Operating Co., Inc. | Barnstall, OK 74002 | Oil & Gas Operator | Apr 2017 |
| 36 | Utah Oil LLC | Rantoul, KS 66079 | Oil Operator | Jun 2025 |