| 401 | The Houston Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Apr 2017 |
| 402 | Thorp Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Feb 2014 |
| 403 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 404 | Total E&P USA, Inc. | Houston, TX 77210 | Oil & Gas Operator | Nov 2011 |
| 405 | Totalfinaelf E&P USA Inc | Houston, TX 77024 | Oil & Gas Operator | Jul 2007 |
| 406 | Touchstone Resources USA, Inc. | Houston, TX 77002 | Oil & Gas Operator | Oct 2006 |
| 407 | Tracker Oil & Gas, Inc. | Bastrop, TX 78602 | Oil & Gas Operator | Apr 2024 |
| 408 | Transtexas Gas Corporation | Houston, TX 77265 | Oil & Gas Operator | Aug 2005 |
| 409 | Trek Oil & Gas, Inc | Houston, TX 77002 | Oil Operator | Mar 1998 |
| 410 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 411 | Tri-C Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Apr 2024 |
| 412 | Tri-Union Development Corp. | Houston, TX 77002 | Oil & Gas Operator | Apr 2024 |
| 413 | Trinity River Energy Oper, LLC | Houston, TX 77008 | Oil & Gas Operator | May 2018 |
| 414 | Trivium Operating, LLC | Fort Worth, TX 76107 | Oil & Gas Operator | Apr 2024 |
| 415 | TX Petroleum Company | Corpus Chrsti, TX 78412 | Oil & Gas Operator | Apr 1996 |
| 416 | U.S. Enercorp, LTD. | San Antonio, TX 78209 | Oil & Gas Operator | Sep 2019 |
| 417 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 418 | United Oil & Minerals L. P. | Austin, TX 78746 | Oil & Gas Operator | Jun 2003 |
| 419 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 420 | United Texas Petroleum Inc. | McKinney, TX 75070 | Oil & Gas Operator | Apr 2024 |
| 421 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Apr 2024 |
| 422 | Valley Gathering Company | Midland, TX 79702 | Oil & Gas Operator | Feb 1997 |
| 423 | Vanguard Operating, LLC | Houston, TX 77057 | Oil & Gas Operator | Feb 2021 |
| 424 | Vantage Operating, LLC | San Antonio, TX 78217 | Oil & Gas Operator | Apr 2024 |
| 425 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Dec 2023 |
| 426 | Ventex Operating Corp. | Addison, TX 75001 | Oil & Gas Operator | Apr 2024 |
| 427 | Virtex Operating Company, Inc. | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Oct 2023 |
| 428 | Virtex Petroleum Company, Inc. | Corpus Chrsti, TX 78477 | Oil & Gas Operator | Jan 2008 |
| 429 | Wadi Operating, LLC | Houston, TX 77079 | Oil & Gas Operator | Apr 2024 |
| 430 | Wadi Petroleum Inc | Houston, TX 77014 | Oil & Gas Operator | May 2018 |
| 431 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Apr 2024 |
| 432 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 433 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 434 | Walbet, Inc. | Monahans, TX 79756 | Oil & Gas Operator | Apr 2024 |
| 435 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Apr 2024 |
| 436 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 437 | Welder Exploration & Prod., Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Dec 2022 |
| 438 | Welder-Heyer Energy, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | Feb 2001 |
| 439 | Western Gulf Oil & Gas Inc. | Dallas, TX 75360 | Oil & Gas Operator | Jul 2000 |
| 440 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 441 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Apr 2024 |
| 442 | Whitesands Operating, L.L.C. | Corpus Chrsti, TX 78466 | Oil & Gas Operator | Apr 2024 |
| 443 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Apr 2024 |
| 444 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Feb 2024 |
| 445 | Whitson, James A., Jr. | Houston, TX 77063 | Oil & Gas Operator | Nov 2011 |
| 446 | Williams, Clayton Energy, Inc. | Houston, TX 77070 | Oil & Gas Operator | Apr 2024 |
| 447 | Williams, Clayton Energy, L.L.C | Midland, TX 79705 | Oil & Gas Operator | May 1993 |
| 448 | Williams, Clayton W., Jr., Inc. | Midland, TX 79705 | Oil & Gas Operator | Mar 2008 |
| 449 | Winchester Energy Operating Co. | Austin, TX 78746 | Oil & Gas Operator | Apr 2024 |
| 450 | Wineland Oil - LLC | Hays, KS 67601 | Oil Operator | Dec 2023 |
| 451 | Winn Exploration Co., Inc. | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Apr 2024 |
| 452 | WJW Operating Co.,LLC | Austin, TX 78738 | Oil & Gas Operator | May 2002 |
| 453 | Wynn-Crosby Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2005 |
| 454 | Wynn-Crosby Operating, LTD. | Dallas, TX 75201 | Oil & Gas Operator | Apr 2024 |
| 455 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Apr 2024 |
| 456 | Zinn Petroleum Co. | Houston, TX 77024 | Oil & Gas Operator | Nov 2021 |