| 301 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 302 | Ultramar Production Company | | Oil & Gas Operator | Dec 1991 |
| 303 | Union Exploration Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 304 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 305 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 306 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 307 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Oct 2025 |
| 308 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 309 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 310 | Upstream Exploration LLC | Metairie, LA 70002 | Oil & Gas Operator | Jan 2020 |
| 311 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Aug 2025 |
| 312 | Vermilion Bay Land Co. | | Oil & Gas Operator | Dec 1994 |
| 313 | Vermilion Resources, Inc. | Houston, TX 77060 | Oil & Gas Operator | Sep 2009 |
| 314 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | May 2025 |
| 315 | Volvo Petroleum, Inc. | | Oil & Gas Operator | Jul 1984 |
| 316 | Vonco Of Mississippi, Inc. | | Oil Operator | Jul 2025 |
| 317 | W. B. McCarter, Jr., Inc. | | Oil & Gas Operator | Dec 1995 |
| 318 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Oct 2025 |
| 319 | Walter T. Lanaux | | Oil & Gas Operator | Nov 1990 |
| 320 | Weaver Exploration Company | | Oil & Gas Operator | Jun 1991 |
| 321 | Will-Drill Production Co., Inc. | Shreveport, LA 71105 | Oil & Gas Operator | Oct 2025 |
| 322 | Williams-Cody, Inc. | Houston, TX 77060 | Oil & Gas Operator | May 1994 |
| 323 | Wle, Inc. | | Oil & Gas Operator | Feb 2012 |
| 324 | Woolf & Magee, Inc. | | Oil & Gas Operator | Oct 1991 |
| 325 | WRT Energy Corporation | Oklahoma City, OK 73118 | Oil & Gas Operator | May 1998 |
| 326 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Oct 2025 |
| 327 | Zilkha Energy Company | Houston, TX 77046 | Oil & Gas Operator | Oct 2002 |