| 601 | Tuthill & Barbee | Amarillo, TX 79101 | Oil & Gas Operator | Nov 1994 |
| 602 | TX Petroleum Company | Corpus Christ, TX 78412 | Oil & Gas Operator | Apr 1996 |
| 603 | U.S. Enercorp, LLC | San Antonio, TX 78217 | Oil & Gas Operator | Jul 2004 |
| 604 | U.S. Enercorp, LTD. | San Antonio, TX 78209 | Oil & Gas Operator | Sep 2019 |
| 605 | U.S.A. Plugging Company | Pearsall, TX 78061 | Oil & Gas Operator | Apr 2026 |
| 606 | Umma Resources, LLC | Portland, TX 78374 | Gas Operator | Apr 2026 |
| 607 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 608 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 609 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Apr 2026 |
| 610 | United Energy Partners, Inc. | Dallas, TX 75201 | Oil & Gas Operator | Mar 2008 |
| 611 | United Oil & Minerals, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jan 2001 |
| 612 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 613 | Upstream Resource Partners, LLC | Elkhart, TX 75839 | Oil Operator | Apr 2026 |
| 614 | Validus Operating Inc. | Port Aransas, TX 78373 | Oil & Gas Operator | Oct 1998 |
| 615 | Valley Gathering Company | Midland, TX 79702 | Oil & Gas Operator | Feb 1997 |
| 616 | Vanguard Operating, LLC | Houston, TX 77057 | Oil & Gas Operator | Aug 2019 |
| 617 | Vaquero Operating | FT Stockton, TX 79735 | Oil & Gas Operator | Apr 2026 |
| 618 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Dec 2025 |
| 619 | Ventum Oil And Gas, LP | Northbrook, IL 60062 | Oil & Gas Operator | Mar 2010 |
| 620 | Venus Oil Company | San Antonio, TX 78209 | Oil & Gas Operator | Dec 2002 |
| 621 | Verdun Oil & Gas LLC | Houston, TX 77024 | Oil & Gas Operator | Apr 2026 |
| 622 | Victoria Operating, Inc. | Victoria, TX 77903 | Oil & Gas Operator | Apr 2026 |
| 623 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Jan 2026 |
| 624 | Viola Production Inc | Dallas, TX 75251 | Oil & Gas Operator | Apr 2026 |
| 625 | Vistatex Energy LLC | Houston, TX 77057 | Oil & Gas Operator | Feb 2026 |
| 626 | VT VIstatex Energy LLC | Houston, TX 77056 | Oil & Gas Operator | Apr 2026 |
| 627 | Wadi Petroleum Inc | Houston, TX 77014 | Oil & Gas Operator | May 2018 |
| 628 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Apr 2026 |
| 629 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 630 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Apr 2026 |
| 631 | Warwick-Artemis, LLC | Nichols Hill, OK 73116 | Oil & Gas Operator | Apr 2026 |
| 632 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 633 | Watusi Energy LLC | Midland, TX 79710 | Oil & Gas Operator | Apr 2026 |
| 634 | Waylander LLC | Plano, TX 75025 | Oil & Gas Operator | Apr 2026 |
| 635 | Welder Exploration & Prod., Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Dec 2022 |
| 636 | Welderxp LTD. | San Antonio, TX 78212 | Oil & Gas Operator | Apr 2026 |
| 637 | Western Gulf Oil & Gas Inc. | Dallas, TX 75360 | Oil & Gas Operator | Jul 2000 |
| 638 | White Creek Energy | Three Rivers, TX 78071 | Oil & Gas Operator | Apr 2026 |
| 639 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Apr 2026 |
| 640 | Whittier Operating Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2007 |
| 641 | Whittington Operating Company | Houston, TX 77069 | Oil & Gas Operator | Apr 2026 |
| 642 | Winn Exploration Co., Inc. | Corpus Christ, TX 78401 | Oil & Gas Operator | Apr 2026 |
| 643 | Wofford, C. J. | El Campo, TX 77437 | Oil & Gas Operator | Apr 2026 |
| 644 | Wynn-Crosby Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2005 |
| 645 | Xeric Oil & Gas Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 2014 |
| 646 | York E & P, LLC | Boling, TX 77420 | Oil & Gas Operator | Apr 2026 |
| 647 | Zenergy Inc | Tulsa, OK 74136 | Oil & Gas Operator | Feb 2026 |
| 648 | Zinke & Trumbo, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2007 |
| 649 | Zinn Petroleum Co. | Houston, TX 77024 | Oil & Gas Operator | Nov 2021 |