| 301 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |
| 302 | Trace Operators, Inc. | | Oil & Gas Operator | Nov 2024 |
| 303 | Transfuel Resources Co | Houston, TX 77215 | Oil & Gas Operator | Aug 2013 |
| 304 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 305 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Oct 2025 |
| 306 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 307 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Oct 2025 |
| 308 | Vernon E. Faulconer | | Oil & Gas Operator | Dec 1996 |
| 309 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | May 2025 |
| 310 | Vitol Resources Inc. Of Delaware | | Oil & Gas Operator | Jul 2016 |
| 311 | W & T Offshore, Inc. | Houston, TX 77057 | Oil & Gas Operator | Oct 2025 |
| 312 | W & T Oil Properties, Inc. | | Oil & Gas Operator | Nov 1989 |
| 313 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Oct 2025 |
| 314 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 315 | WCC Energy Group LLC | | Oil & Gas Operator | Dec 2024 |
| 316 | Weaver Exploration Company | | Oil & Gas Operator | Jun 1991 |
| 317 | Westland Oil Development Corp. | Conroe, TX 77305 | Oil & Gas Operator | Mar 2008 |
| 318 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Oct 2025 |
| 319 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 320 | Whitton Company, Inc. | | Oil & Gas Operator | Jul 2020 |
| 321 | Wichita River Oil Corporation | Englewood, CO 80111 | Oil & Gas Operator | Apr 2009 |
| 322 | Windham Oil Company | | Oil & Gas Operator | Dec 1987 |
| 323 | Wintershall Corporation | | Oil & Gas Operator | Oct 1989 |
| 324 | Wle, Inc. | | Oil & Gas Operator | Feb 2012 |
| 325 | Woolf & Magee, Inc. | | Oil & Gas Operator | Oct 1991 |
| 326 | WRT Energy Corporation | Oklahoma City, OK 73118 | Oil & Gas Operator | May 1998 |
| 327 | Yuma Petroleum Company | Houston, TX 77027 | Oil & Gas Operator | Aug 2002 |
| 328 | Zenergy Operating Company, LLC | Tulsa, OK 74136 | Oil & Gas Operator | Dec 2016 |
| 329 | Zgen, Inc. | | Oil & Gas Operator | Jul 1990 |