| 501 | Southwest Investment Fund, Inc. | Dallas, TX 75229 | Oil & Gas Operator | Aug 2003 |
| 502 | Southwest Oil & Land, Inc. | Corpus Chrsti, TX 78460 | Oil & Gas Operator | Dec 1999 |
| 503 | Southwestern Energy Prod Co | Houston, TX 77032 | Oil & Gas Operator | Jun 2015 |
| 504 | Sparta Exploration LLC | Houston, TX 77279 | Oil & Gas Operator | Dec 2025 |
| 505 | Spiller Operating Co., Inc. | Round Rock, TX 78665 | Oil & Gas Operator | May 2015 |
| 506 | Spindletop Drilling Co. | Dallas, TX 75230 | Oil & Gas Operator | Dec 2025 |
| 507 | Star Production, Inc. | Dallas, TX 75360 | Oil & Gas Operator | Dec 2025 |
| 508 | Stephens Production Company | The Woodlands, TX 77381 | Oil & Gas Operator | Oct 2025 |
| 509 | Stewardship Resources | Roanoke, TX 76262 | Oil & Gas Operator | Jun 2022 |
| 510 | Stone, J. G. Oil Co. | Victoria, TX 77904 | Oil & Gas Operator | Sep 2018 |
| 511 | Strata Operating, Inc. | Corpus Chrsti, TX 78466 | Oil & Gas Operator | Dec 2025 |
| 512 | Stratco Operating Co Inc | Austin, TX 78701 | Oil & Gas Operator | Dec 2025 |
| 513 | Sue-Ann Operating, L.C. | Victoria, TX 77903 | Oil & Gas Operator | Dec 2025 |
| 514 | Sue-Ann Production Company | Victoria, TX 77903 | Oil & Gas Operator | Mar 2008 |
| 515 | Suemaur Expl. & Prod., LLC | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Jun 2024 |
| 516 | Suemaur Exploration, Inc. | Corpus Chrsti, TX 78470 | Oil & Gas Operator | Mar 2008 |
| 517 | Suncoast Technical Services Inc | Dallas, TX 75251 | Oil & Gas Operator | Dec 2025 |
| 518 | Sundown Energy LP | Dallas, TX 75248 | Oil & Gas Operator | Dec 2025 |
| 519 | Sundown Energy, Inc. | Dallas, TX 75240 | Oil & Gas Operator | May 2025 |
| 520 | Superior Oil & Gas Invt, L.L.C. | Conroe, TX 77305 | Gas Operator | Jul 2018 |
| 521 | Sure Flow Oil & Gas Company | Victoria, TX 77902 | Oil & Gas Operator | Mar 2008 |
| 522 | Sure Flow Oil & Gas, Inc. | Victoria, TX 77902 | Oil & Gas Operator | Dec 2025 |
| 523 | Swift Energy Company | Houston, TX 77060 | Oil & Gas Operator | Mar 2021 |
| 524 | Swope Corp. | Austin, TX 78735 | Oil & Gas Operator | Dec 2025 |
| 525 | Sydri Operating, LLC | Dallas, TX 75231 | Oil & Gas Operator | Dec 2025 |
| 526 | T & T Production Co. | Victoria, TX 77902 | Oil & Gas Operator | Feb 1995 |
| 527 | T - C Oil Company | Refugio, TX 78377 | Oil & Gas Operator | Jan 2012 |
| 528 | T-C Oil Company, LLC | Refugio, TX 78377 | Oil & Gas Operator | Dec 2025 |
| 529 | Talon Development Company | Boerne, TX 78006 | Oil & Gas Operator | Sep 2007 |
| 530 | Taos Resources Operating Co LLC | Houston, TX 77037 | Oil & Gas Operator | Dec 2019 |
| 531 | TBC Petroleum | Cuero, TX 77954 | Oil & Gas Operator | Sep 2023 |
| 532 | Team Operating, L.L.C. | Pinehurst, TX 77362 | Oil & Gas Operator | Dec 2025 |
| 533 | Tejas Operating LLC | Houston, TX 77056 | Oil & Gas Operator | Dec 2025 |
| 534 | Tepee Petroleum Company, Inc. | Houston, TX 77098 | Oil & Gas Operator | Feb 2014 |
| 535 | Texaco E & P Inc. | Houston, TX 77099 | Oil & Gas Operator | Dec 2025 |
| 536 | Texas Fuel Company | Galveston, TX 77550 | Oil & Gas Operator | Dec 2025 |
| 537 | Texas Operating Partners LLC | Tomball, TX 77377 | Oil & Gas Operator | Dec 2025 |
| 538 | Texcal Energy (GP) LLC | Denver, CO 80202 | Oil & Gas Operator | Mar 2016 |
| 539 | Texlan Oil Company, Inc. | Tyler, TX 75701 | Oil & Gas Operator | Nov 1994 |
| 540 | Texstar North America, Inc. | Waynesboro, MS 39367 | Oil & Gas Operator | Aug 1994 |
| 541 | Three Mile Joint Venture | Houston, TX 77027 | Oil & Gas Operator | Jul 1995 |
| 542 | Thunderbird Energy, Inc. | Norman, OK 73069 | Oil & Gas Operator | Dec 2025 |
| 543 | Tidal Petroleum, Inc. | Schertz, TX 78154 | Oil & Gas Operator | Dec 2025 |
| 544 | Tide Energy, Inc. | Dallas, TX 75206 | Gas Operator | Oct 1994 |
| 545 | Tidemark Petroleum, Inc. | San Antonio, TX 78209 | Oil & Gas Operator | Jul 2002 |
| 546 | Tiger Resources, L.L.C. | Houston, TX 77070 | Oil & Gas Operator | Feb 2004 |
| 547 | Titan Resources I, Inc. | Midland, TX 79701 | Oil & Gas Operator | Jun 2000 |
| 548 | Top Op, L.L.C. | Houston, TX 77077 | Oil & Gas Operator | May 2020 |
| 549 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 550 | TPR - Texas Petroleum Res. Inc | Dallas, TX 75201 | Oil & Gas Operator | Dec 2025 |
| 551 | Trans-Pecos Resources, Inc. | Houston, TX 77056 | Oil & Gas Operator | Dec 2025 |
| 552 | Transtexas Gas Corporation | Houston, TX 77265 | Oil & Gas Operator | Aug 2005 |
| 553 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 554 | Tri-C Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Dec 2025 |
| 555 | Tri-Union Development Corp. | Houston, TX 77002 | Oil & Gas Operator | Dec 2025 |
| 556 | Triad Energy Corporation | Houston, TX 77057 | Oil & Gas Operator | Oct 2011 |
| 557 | Triangle Three Resources L.L.C. | Dallas, TX 75240 | Oil & Gas Operator | Oct 2024 |
| 558 | Trident Corporation | Woodsboro, TX 78393 | Oil & Gas Operator | Dec 2025 |
| 559 | Trinity Resources, Inc. | Houston, TX 77277 | Oil & Gas Operator | May 2020 |
| 560 | Triple L Oil Company | Corpus Chrsti, TX 78469 | Oil & Gas Operator | Jan 1998 |
| 561 | Triton Oil & Gas Corp. | Houston, TX 77002 | Oil & Gas Operator | Nov 2014 |
| 562 | Tschoepe, Arthur J. | Leakey, TX 78873 | Oil & Gas Operator | Jun 2001 |
| 563 | TT Operating, LLC | Kilgore, TX 75663 | Oil & Gas Operator | Dec 2025 |
| 564 | Tucker Operating Co., Inc. | Victoria, TX 77903 | Oil & Gas Operator | Dec 2025 |
| 565 | TX Petroleum Company | Corpus Chrsti, TX 78412 | Oil & Gas Operator | Apr 1996 |
| 566 | Ultra Oil & Gas, Inc. | Centerton, AR 72719 | Oil & Gas Operator | Dec 2025 |
| 567 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 568 | Unicorn Energy, Inc. | Elgin, TX 78621 | Oil & Gas Operator | Dec 2025 |
| 569 | Union Crude Company | Baytown, TX 77521 | Oil & Gas Operator | Apr 2018 |
| 570 | Union Gas Operating Company | Spring, TX 77391 | Oil & Gas Operator | Dec 2025 |
| 571 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 572 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Dec 2025 |
| 573 | United Oil & Minerals, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jan 2001 |
| 574 | United Operating, LLC *** | Midland, TX 79710 | Oil & Gas Operator | Dec 2025 |
| 575 | Unoso Operating Company L.L.C. | Georgetown, TX 78633 | Oil & Gas Operator | Dec 2025 |
| 576 | Upda Operators, Inc. | Jacksboro, TX 76458 | Oil & Gas Operator | Dec 2009 |
| 577 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Dec 2025 |
| 578 | Valence Operating Company | Kingwood, TX 77339 | Oil & Gas Operator | Dec 2025 |
| 579 | Valerius, Inc. & Zine, Inc. | Corpus Chrsti, TX 78473 | Oil & Gas Operator | Jul 1994 |
| 580 | Valerius, Robert D. Inc. | Corpus Chrsti, TX 78473 | Oil & Gas Operator | Aug 2003 |
| 581 | Valley Gathering Company | Midland, TX 79702 | Oil & Gas Operator | Feb 1997 |
| 582 | Vantage Operating, LLC | San Antonio, TX 78230 | Oil & Gas Operator | Dec 2025 |
| 583 | Vaquero Oil & Gas, Inc. | League City, TX 77573 | Oil & Gas Operator | Aug 2008 |
| 584 | Venus Oil Company | San Antonio, TX 78209 | Oil & Gas Operator | Dec 2002 |
| 585 | Verus Energy, Inc | Houston, TX 77098 | Oil & Gas Operator | Sep 2004 |
| 586 | Victoria Operating, Inc. | Victoria, TX 77903 | Oil & Gas Operator | Dec 2025 |
| 587 | Viola Production Inc | Dallas, TX 75251 | Oil & Gas Operator | Dec 2025 |
| 588 | Viper S.W.D., LLC | El Campo, TX 77437 | Oil & Gas Operator | Dec 2025 |
| 589 | Virtex Petroleum Company, Inc. | Corpus Chrsti, TX 78477 | Oil & Gas Operator | Jan 2008 |
| 590 | Wadi Petroleum Inc | Houston, TX 77014 | Oil & Gas Operator | May 2018 |
| 591 | Waelder Oil & Gas, Inc. | Fort Smith, AR 72903 | Oil & Gas Operator | Sep 2025 |
| 592 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 593 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 594 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Dec 2025 |
| 595 | Walter Exploration Company | Dallas, TX 75206 | Oil & Gas Operator | Dec 2025 |
| 596 | Walter Exploration Inc | Dallas, TX 75206 | Oil & Gas Operator | May 2009 |
| 597 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 598 | Weibye, Carolyn S. | Houston, TX 77098 | Oil & Gas Operator | Dec 2025 |
| 599 | Welder Operating, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | Mar 2001 |
| 600 | Welder-Heyer Energy, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | Feb 2001 |