| 601 | U.S. Enercorp, LTD. | San Antonio, TX 78209 | Oil & Gas Operator | Sep 2019 |
| 602 | U.S.A. Plugging Company | Pearsall, TX 78061 | Oil & Gas Operator | Jul 2025 |
| 603 | Umma Resources, LLC | Portland, TX 78374 | Gas Operator | Jul 2025 |
| 604 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 605 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 606 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Jul 2025 |
| 607 | United Energy Partners, Inc. | Dallas, TX 75201 | Oil & Gas Operator | Mar 2008 |
| 608 | United Oil & Minerals, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jan 2001 |
| 609 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 610 | Upstream Resource Partners, LLC | Elkhart, TX 75839 | Oil Operator | Jul 2025 |
| 611 | Validus Operating Inc. | Port Aransas, TX 78373 | Oil & Gas Operator | Oct 1998 |
| 612 | Valley Gathering Company | Midland, TX 79702 | Oil & Gas Operator | Feb 1997 |
| 613 | Vanguard Operating, LLC | Houston, TX 77057 | Oil & Gas Operator | Feb 2021 |
| 614 | Vaquero Operating | FT Stockton, TX 79735 | Oil & Gas Operator | Jul 2025 |
| 615 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Mar 2025 |
| 616 | Ventum Oil And Gas, LP | Northbrook, IL 60062 | Oil & Gas Operator | Mar 2010 |
| 617 | Venus Oil Company | San Antonio, TX 78209 | Oil & Gas Operator | Dec 2002 |
| 618 | Verdun Oil & Gas LLC | Houston, TX 77024 | Oil & Gas Operator | Jul 2025 |
| 619 | Victoria Operating, Inc. | Victoria, TX 77903 | Oil & Gas Operator | Jul 2025 |
| 620 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Apr 2025 |
| 621 | Viola Production Inc | Dallas, TX 75251 | Oil & Gas Operator | Jul 2025 |
| 622 | Vistatex Energy LLC | Houston, TX 77057 | Oil & Gas Operator | Apr 2025 |
| 623 | VT VIstatex Energy LLC | Houston, TX 77056 | Oil & Gas Operator | Jul 2025 |
| 624 | Wadi Petroleum Inc | Houston, TX 77014 | Oil & Gas Operator | May 2018 |
| 625 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Jul 2025 |
| 626 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 627 | Wallis Energy, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jul 2025 |
| 628 | Warwick-Artemis, LLC | Nichols Hill, OK 73116 | Oil & Gas Operator | Jul 2025 |
| 629 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 630 | Waylander LLC | Plano, TX 75025 | Oil & Gas Operator | Jul 2025 |
| 631 | Welder Exploration & Prod., Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Dec 2022 |
| 632 | Welderxp LTD. | San Antonio, TX 78212 | Oil & Gas Operator | Jul 2025 |
| 633 | Western Gulf Oil & Gas Inc. | Dallas, TX 75360 | Oil & Gas Operator | Jul 2000 |
| 634 | White Creek Energy | Three Rivers, TX 78071 | Oil & Gas Operator | Jul 2025 |
| 635 | White Creek Energy, Inc. | San Antonio, TX 78246 | Oil & Gas Operator | Dec 2003 |
| 636 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Jul 2025 |
| 637 | Whittier Operating Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2007 |
| 638 | Whittington Operating Company | Houston, TX 77069 | Oil & Gas Operator | Jul 2025 |
| 639 | Winn Exploration Co., Inc. | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Jul 2025 |
| 640 | Wofford, C. J. | El Campo, TX 77437 | Oil & Gas Operator | Jul 2025 |
| 641 | Wynn-Crosby Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2005 |
| 642 | Xeric Oil & Gas Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 2014 |
| 643 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Jul 2025 |
| 644 | York E & P, LLC | Boling, TX 77420 | Oil & Gas Operator | Jul 2025 |
| 645 | Zenergy Inc | Tulsa, OK 74136 | Oil & Gas Operator | May 2025 |
| 646 | Zinke & Trumbo, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2007 |
| 647 | Zinn Petroleum Co. | Houston, TX 77024 | Oil & Gas Operator | Nov 2021 |