| 501 | Texas Meridian Res. Expl., Inc. | Houston, TX 77079 | Oil & Gas Operator | Jun 1998 |
| 502 | Texas Western Energy Corporation | Portland, TX 78374 | Oil & Gas Operator | Nov 2002 |
| 503 | Texegy Operating Company LLC | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Dec 2024 |
| 504 | Texian Operating Company, LLC | Irving, TX 75063 | Oil & Gas Operator | Feb 2026 |
| 505 | Texstar North America, Inc. | Waynesboro, MS 39367 | Oil & Gas Operator | Aug 1994 |
| 506 | Titan Energy Operating LLC | Houston, TX 77056 | Oil Operator | Jan 2016 |
| 507 | Tiza Energy, Inc. | Austin, TX 78715 | Oil & Gas Operator | Feb 2026 |
| 508 | TNR Petroleum, Inc. | Austin, TX 78747 | Oil & Gas Operator | Sep 1999 |
| 509 | Tracer Energy, Inc. | Graham, TX 76450 | Oil & Gas Operator | Nov 1998 |
| 510 | Traton Operating Company | Kingwood, TX 77339 | Oil & Gas Operator | Mar 2019 |
| 511 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 512 | Tri-C Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Feb 2026 |
| 513 | Trinidad Energy, LLC | Midland, TX 79708 | Oil & Gas Operator | Feb 2026 |
| 514 | Trinidad Resources, LLC | San Antonio, TX 78217 | Oil & Gas Operator | Feb 2026 |
| 515 | True Oil Company | Casper, WY 82602 | Oil & Gas Operator | Aug 2003 |
| 516 | Tryco Exploration, LLC | Plano, TX 75026 | Oil & Gas Operator | Nov 2006 |
| 517 | Tucker Operating Co., Inc. | Victoria, TX 77903 | Oil & Gas Operator | Feb 2026 |
| 518 | Txla Energy, Inc. | Houston, TX 77018 | Oil & Gas Operator | Feb 2026 |
| 519 | U.S.A. Plugging Company | Pearsall, TX 78061 | Oil & Gas Operator | Feb 2026 |
| 520 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 521 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 522 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 523 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Feb 2026 |
| 524 | United Oil & Minerals L. P. | Austin, TX 78746 | Oil & Gas Operator | Jun 2003 |
| 525 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Feb 2026 |
| 526 | Ventex Operating Corp. | Addison, TX 75001 | Oil & Gas Operator | Feb 2026 |
| 527 | Venus Oil Company | San Antonio, TX 78209 | Oil & Gas Operator | Dec 2002 |
| 528 | Veracity Energy LLC | The Woodlands, TX 77380 | Oil & Gas Operator | Aug 2023 |
| 529 | Viceroy Petroleum, LP | College Sta, TX 77845 | Oil & Gas Operator | Feb 2026 |
| 530 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |
| 531 | Viper S.W.D., LLC | El Campo, TX 77437 | Oil & Gas Operator | Feb 2026 |
| 532 | Virlar Exploration, Inc. | Houston, TX 77227 | Oil & Gas Operator | Aug 1995 |
| 533 | Wagner & Brown, LTD. | Midland, TX 79702 | Oil & Gas Operator | Aug 2014 |
| 534 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 535 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 536 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Feb 2026 |
| 537 | Walter Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 538 | Wapiti Operating, LLC | Houston, TX 77043 | Oil & Gas Operator | Feb 2026 |
| 539 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 540 | Welder Exploration & Prod., Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Dec 2022 |
| 541 | Welderxp LTD. | San Antonio, TX 78212 | Oil & Gas Operator | Feb 2026 |
| 542 | Well-Co Solutions, LLC | Batson, TX 77519 | Oil Operator | Feb 2026 |
| 543 | Westland Oil Development Corp. | Conroe, TX 77305 | Oil & Gas Operator | Mar 2008 |
| 544 | Weststar Oil & Gas Inc | Edmond, OK 73013 | Oil & Gas Operator | Dec 2025 |
| 545 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Feb 2026 |
| 546 | Whitehead Prod. Co., Inc. | Humble, TX 77338 | Oil & Gas Operator | Dec 2025 |
| 547 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 548 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 549 | Whitmar Exploration Company | Denver, CO 80202 | Oil & Gas Operator | Nov 2025 |
| 550 | Wilmoth Interests, Inc. | Marion Center, PA 15759 | Oil & Gas Operator | Dec 2025 |
| 551 | Wing Corporation | Houston, TX 77002 | Oil & Gas Operator | Jun 2000 |
| 552 | Wofford, C. J. | El Campo, TX 77437 | Oil & Gas Operator | Feb 2026 |
| 553 | Wood Energy Corporation | Baytown, TX 77520 | Oil & Gas Operator | Jun 1999 |
| 554 | Woodard Energy Company | Houston, TX 77042 | Oil & Gas Operator | Mar 2010 |
| 555 | Wynn-Crosby Operating, LTD. | Dallas, TX 75201 | Oil & Gas Operator | Feb 2026 |
| 556 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Feb 2026 |
| 557 | Zachry Exploration, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | Feb 2026 |
| 558 | Zachry Exploration, LLC | San Antonio, TX 78224 | Oil & Gas Operator | Feb 2026 |
| 559 | Zachry Exploration, LTD. | San Antonio, TX 78205 | Oil & Gas Operator | Jan 2009 |
| 560 | Zenergy Inc | Tulsa, OK 74136 | Oil & Gas Operator | Dec 2025 |
| 561 | Zinke & Trumbo, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2007 |
| 562 | Zinn Petroleum Co. | Houston, TX 77024 | Oil & Gas Operator | Nov 2021 |