| 301 | Transamerican Energy/Toce Oil | | Oil & Gas Operator | Dec 1994 |
| 302 | Transamerican-Swepi-Toce Oil | | Oil & Gas Operator | Apr 1990 |
| 303 | Trinity Resources, Inc. | Houston, TX 77277 | Oil & Gas Operator | May 2020 |
| 304 | Triton Oil & Gas Corp. | Houston, TX 77002 | Oil & Gas Operator | Nov 2014 |
| 305 | Triumph Energy, Inc. | Lafayette, LA 70505 | Oil & Gas Operator | Nov 2015 |
| 306 | TXP Operating Company | | Oil & Gas Operator | Jul 1992 |
| 307 | U S Exploraton Liq Trust | | Oil & Gas Operator | Oct 1994 |
| 308 | U.S. Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 309 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 310 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 311 | Union Exploration Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 312 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 313 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 314 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 315 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 316 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 317 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Oct 2025 |
| 318 | Vernon E. Faulconer | | Oil & Gas Operator | Dec 1996 |
| 319 | Vernon E. Faulconer, Inc. | Tyler, TX 75711 | Oil & Gas Operator | Dec 2024 |
| 320 | Vinbar Oil & Gas, LLC | | Oil & Gas Operator | Jan 2018 |
| 321 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | May 2025 |
| 322 | W. L. Estis | | Oil & Gas Operator | Dec 1999 |
| 323 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Oct 2025 |
| 324 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 325 | Wayman W. Buchanan | | Oil & Gas Operator | Feb 1986 |
| 326 | Weaver Exploration Company | | Oil & Gas Operator | Jun 1991 |
| 327 | Westland Oil Development Corp. | Conroe, TX 77305 | Oil & Gas Operator | Mar 2008 |
| 328 | Whiskey Bay Oil Company | | Oil & Gas Operator | May 1990 |
| 329 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Oct 2025 |
| 330 | White Rock Oil & Gas, LLC | Plano, TX 75024 | Oil & Gas Operator | Oct 2025 |
| 331 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 332 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 333 | Williams-Cody, Inc. | Houston, TX 77060 | Oil & Gas Operator | May 1994 |
| 334 | Wle, Inc. | | Oil & Gas Operator | Feb 2012 |
| 335 | Woodbine Petroleum, Inc. | Dallas, TX 75204 | Oil & Gas Operator | Aug 2003 |
| 336 | Xeric Oil & Gas Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 2014 |
| 337 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Oct 2025 |
| 338 | Yentzen Production, Inc. | | Oil Operator | Mar 1987 |
| 339 | Yuma Petroleum Company | Houston, TX 77027 | Oil & Gas Operator | Aug 2002 |
| 340 | Zachry Exploration, LLC | San Antonio, TX 78224 | Oil & Gas Operator | Oct 2025 |
| 341 | Zeit Exploration Co., Inc. | | Oil & Gas Operator | May 1994 |