| 601 | Transamerican Natural Gas Corp. | Houston, TX 77032 | Oil & Gas Operator | Aug 2000 |
| 602 | Transtexas Gas Corporation | Houston, TX 77265 | Oil & Gas Operator | Aug 2005 |
| 603 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 604 | Trinity Operating (Usg), LLC | Houston, TX 77002 | Oil & Gas Operator | Aug 2025 |
| 605 | Trinity River Energy Oper, LLC | Houston, TX 77008 | Oil & Gas Operator | May 2018 |
| 606 | Tristar Oil & Gas | Freer, TX 78357 | Oil & Gas Operator | Aug 2025 |
| 607 | Trium, LTD. | Laredo, TX 78041 | Oil Operator | Aug 2025 |
| 608 | Troubadour Operating, LLC | Houston, TX 77019 | Oil & Gas Operator | Aug 2025 |
| 609 | TX Petroleum Company | Corpus Chrsti, TX 78412 | Oil & Gas Operator | Apr 1996 |
| 610 | Txco Resources Inc. | San Antonio, TX 78280 | Oil & Gas Operator | Aug 2025 |
| 611 | U. S. Operating, Inc. | Dallas, TX 75252 | Oil & Gas Operator | Aug 2025 |
| 612 | U.S. Enercorp, LTD. | San Antonio, TX 78209 | Oil & Gas Operator | Sep 2019 |
| 613 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 614 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 615 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Aug 2025 |
| 616 | United Oil & Minerals L. P. | Austin, TX 78746 | Oil & Gas Operator | Jun 2003 |
| 617 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 618 | United World Energy, Inc. | Aurora, CO 80040 | Oil & Gas Operator | Aug 2025 |
| 619 | Unitex Oil & Gas, L.L.C. | Midland, TX 79701 | Oil & Gas Operator | Aug 2025 |
| 620 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Aug 2025 |
| 621 | Valence Operating Company | Kingwood, TX 77339 | Oil & Gas Operator | Aug 2025 |
| 622 | Vaquero Operating | FT Stockton, TX 79735 | Oil & Gas Operator | Aug 2025 |
| 623 | Vaquillas Operating, Inc. | Laredo, TX 78041 | Oil & Gas Operator | Dec 2002 |
| 624 | Varas Energy Operating Company, LLC | Houston, TX 77005 | Oil & Gas Operator | Aug 2025 |
| 625 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Apr 2025 |
| 626 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | May 2025 |
| 627 | Vintage Petroleum, LLC | Houston, TX 77210 | Oil & Gas Operator | Dec 2019 |
| 628 | Viper S.W.D., LLC | El Campo, TX 77437 | Oil & Gas Operator | Aug 2025 |
| 629 | Virtex Operating Company, Inc. | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Oct 2023 |
| 630 | Virtex Petroleum Company, Inc. | Corpus Chrsti, TX 78477 | Oil & Gas Operator | Jan 2008 |
| 631 | Vision Oil And Gas LLC | Laredo, TX 78041 | Oil & Gas Operator | Aug 2025 |
| 632 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Aug 2025 |
| 633 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 634 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Aug 2025 |
| 635 | Warbonnet Exploration Company | Houston, TX 77056 | Oil & Gas Operator | Apr 2016 |
| 636 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 637 | Weaver & Sharp | Corpus Chrsti, TX 78403 | Oil & Gas Operator | Mar 1997 |
| 638 | Weeks Exploration Company | Houston, TX 77063 | Oil & Gas Operator | Aug 1995 |
| 639 | Welhausen Operating Co., Inc. | Beeville, TX 78104 | Oil & Gas Operator | Aug 2003 |
| 640 | Welhausen Operating Company, LP | Beeville, TX 78104 | Oil & Gas Operator | Nov 2016 |
| 641 | West Petroleum Corp. | San Antonio, TX 78205 | Oil & Gas Operator | Oct 2009 |
| 642 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 643 | White Marlin Operating Company, LLC | Houston, TX 77002 | Oil & Gas Operator | Aug 2025 |
| 644 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Aug 2025 |
| 645 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 646 | Whittier Operating Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2007 |
| 647 | Wilbanks, Bruce A. Company | Midland, TX 79702 | Oil & Gas Operator | Aug 2025 |
| 648 | Wilmoth Interests, Inc. | Marion Center, PA 15759 | Oil & Gas Operator | Mar 2025 |
| 649 | Wilson Hydrocarbon Inc. | Houston, TX 77066 | Oil & Gas Operator | Aug 2025 |
| 650 | Winchester Production Company | Shreveport, LA 71129 | Oil & Gas Operator | Nov 2008 |
| 651 | Wiseman, B. W., Jr. | Midland, TX 79702 | Oil & Gas Operator | Dec 2002 |
| 652 | World Energy Corporation | Laredo, TX 78041 | Oil & Gas Operator | Aug 2003 |
| 653 | Wright Brothers Energy, Inc. | Boerne, TX 78006 | Oil & Gas Operator | Aug 2025 |
| 654 | Wright Brothers Petroleum, LTD. | San Antonio, TX 78212 | Oil & Gas Operator | May 2002 |
| 655 | XCL-Texas, Inc. | Lafayette, LA 70503 | Oil & Gas Operator | Nov 2000 |
| 656 | Xeric Oil & Gas Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 2014 |
| 657 | Xog Operating LLC | Midland, TX 79702 | Oil & Gas Operator | Aug 2025 |
| 658 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Aug 2025 |
| 659 | Yarborough Oil & Gas L.P. | Midland, TX 79701 | Oil & Gas Operator | Oct 2000 |
| 660 | Yarborough, W. B. | Midland, TX 79701 | Oil & Gas Operator | Nov 1995 |
| 661 | Zachry Exploration, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | Aug 2025 |
| 662 | Zachry Exploration, LLC | San Antonio, TX 78224 | Oil & Gas Operator | Aug 2025 |
| 663 | Zachry Exploration, LTD. | San Antonio, TX 78205 | Oil & Gas Operator | Jan 2009 |
| 664 | Zachry, H. B. Company | San Antonio, TX 78205 | Oil & Gas Operator | Apr 1994 |
| 665 | Zaf Oil | San Antonio, TX 78230 | Oil & Gas Operator | Aug 2002 |
| 666 | Zone Energy, LLC | Houston, TX 77251 | Oil & Gas Operator | Jan 2025 |