| 501 | TNT Petroleum Company, Inc. | Corpus Chrsti, TX 78473 | Oil & Gas Operator | Feb 1996 |
| 502 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 503 | Total E&P USA, Inc. | Houston, TX 77210 | Oil & Gas Operator | Nov 2011 |
| 504 | Totalfinaelf E&P USA Inc | Houston, TX 77024 | Oil & Gas Operator | Jul 2007 |
| 505 | Townsend Company | Abilene, TX 79608 | Oil & Gas Operator | Dec 2021 |
| 506 | Trailblazer Energy Resources, LLC | Tulsa, OK 74136 | Oil & Gas Operator | Apr 2025 |
| 507 | Trans-Pecos Resources, Inc. | Houston, TX 77056 | Oil & Gas Operator | Apr 2025 |
| 508 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 509 | Tri-C Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Apr 2025 |
| 510 | Triad Energy Corporation | Houston, TX 77057 | Oil & Gas Operator | Oct 2011 |
| 511 | Trident Corporation | Woodsboro, TX 78393 | Oil & Gas Operator | Apr 2025 |
| 512 | Trinity Resources, Inc. | Houston, TX 77277 | Oil & Gas Operator | May 2020 |
| 513 | Triple 'A' Energy, Inc. | Boerne, TX 78006 | Oil & Gas Operator | Apr 2025 |
| 514 | Triple L Oil Company | Corpus Chrsti, TX 78469 | Oil & Gas Operator | Jan 1998 |
| 515 | Truth Resources LP | Houston, TX 77090 | Oil Operator | Sep 2021 |
| 516 | Union Crude Company | Baytown, TX 77521 | Oil & Gas Operator | Apr 2018 |
| 517 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 518 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Apr 2025 |
| 519 | United Energy Corporation | San Antonio, TX 78209 | Oil & Gas Operator | Apr 2025 |
| 520 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Apr 2025 |
| 521 | Vanguard Operating, LLC | Houston, TX 77057 | Oil & Gas Operator | Feb 2021 |
| 522 | Vantage Operating, LLC | San Antonio, TX 78230 | Oil & Gas Operator | Apr 2025 |
| 523 | Venus Exploration, Inc. | San Antonio, TX 78209 | Oil & Gas Operator | Jul 2013 |
| 524 | Viola Prod., Inc. | Dallas, TX 75251 | Oil & Gas Operator | Apr 2025 |
| 525 | Virlar Exploration, Inc. | Houston, TX 77227 | Oil & Gas Operator | Aug 1995 |
| 526 | Virtex Operating Company, Inc. | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Oct 2023 |
| 527 | Virtex Petroleum Company, Inc. | Corpus Chrsti, TX 78477 | Oil & Gas Operator | Jan 2008 |
| 528 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Apr 2025 |
| 529 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 530 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 531 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Apr 2025 |
| 532 | Wapiti Operating, LLC | Houston, TX 77043 | Oil & Gas Operator | Apr 2025 |
| 533 | Ward, E. B. | Alice, TX 78333 | Oil & Gas Operator | Jun 2001 |
| 534 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 535 | Welder Exploration & Prod., Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Dec 2022 |
| 536 | Welderxp LTD. | San Antonio, TX 78212 | Oil & Gas Operator | Apr 2025 |
| 537 | West Tuleta Operating Corp. | Tuleta, TX 78162 | Oil & Gas Operator | May 2019 |
| 538 | Westridge Oil & Gas Properties | Mineral Wells, TX 76068 | Oil & Gas Operator | Apr 2025 |
| 539 | White Marlin Operating Company, LLC | Houston, TX 77002 | Oil & Gas Operator | Apr 2025 |
| 540 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Apr 2025 |
| 541 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 542 | Whittington Operating Company | Houston, TX 77069 | Oil & Gas Operator | Apr 2025 |
| 543 | Wild Cat Operating Company | Victoria, TX 77903 | Oil & Gas Operator | Mar 2008 |
| 544 | Winn Exploration Co., Inc. | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Apr 2025 |
| 545 | Wiser Oil Co | Denver, CO 80202 | Oil & Gas Operator | Dec 2023 |
| 546 | Wofford, C. J. | El Campo, TX 77437 | Oil & Gas Operator | Apr 2025 |
| 547 | Wynn-Crosby Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2005 |
| 548 | Wynn-Crosby Operating, LTD. | Dallas, TX 75201 | Oil & Gas Operator | Apr 2025 |
| 549 | Xeric Oil & Gas Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 2014 |
| 550 | Xog Operating LLC | Midland, TX 79702 | Oil & Gas Operator | Apr 2025 |
| 551 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Apr 2025 |
| 552 | Yuma E & P Company, Inc. | Houston, TX 77027 | Oil & Gas Operator | Apr 2025 |