| 601 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |
| 602 | Trace Operators, Inc. | | Oil & Gas Operator | Nov 2024 |
| 603 | Trafalgar House Oil & Gas Inc. | Houston, TX 77002-7346 | Oil & Gas Operator | Jan 1992 |
| 604 | Trans Ocean Oil, Inc. | Houston, TX 77252 | Oil & Gas Operator | Sep 1980 |
| 605 | Transcontinental Oil Corp. | | Oil & Gas Operator | Sep 1985 |
| 606 | Tri-Union Development Corp. | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 607 | Triad Energy Corp. Of Texas | Houston, TX 77057-2696 | Oil & Gas Operator | Sep 2014 |
| 608 | Trinity Resources, Inc. | Houston, TX 77277 | Oil & Gas Operator | May 2020 |
| 609 | Triumph Energy, Inc. | Lafayette, LA 70505 | Oil & Gas Operator | Nov 2015 |
| 610 | Two Bayous, Inc. | | Oil & Gas Operator | Dec 2024 |
| 611 | Txo Production Corp. | Ganado, TX 77962 | Oil & Gas Operator | Aug 2022 |
| 612 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 613 | Union Exploration Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 614 | Union Gas Operating Company | Houston, TX 77014 | Oil & Gas Operator | May 2025 |
| 615 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 616 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 617 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 618 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 619 | United Operators, Inc. | | Oil Operator | Sep 1999 |
| 620 | United Petroleum Corporation | Edgwater, CO 80214 | Oil & Gas Operator | May 1996 |
| 621 | Universal Drilling Co., Inc. | Denver, CO 80203 | Oil & Gas Operator | Sep 2003 |
| 622 | Unocal Exploration Corporation | | Oil & Gas Operator | May 1992 |
| 623 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | May 2025 |
| 624 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Mar 2025 |
| 625 | Van Operating, LTD. | Albany, TX 76430 | Oil & Gas Operator | May 2025 |
| 626 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Jan 2025 |
| 627 | Vega Oil & Gas MGMT., Inc. | | Oil & Gas Operator | Aug 1981 |
| 628 | Venture Oil Company Of Texas | | Oil Operator | Sep 1988 |
| 629 | Verado Energy, Inc. | Allen, TX 75013 | Oil & Gas Operator | May 2025 |
| 630 | Vernon E. Faulconer | | Oil & Gas Operator | Dec 1996 |
| 631 | Vernon E. Faulconer, Inc. | Tyler, TX 75711 | Oil & Gas Operator | Dec 2024 |
| 632 | Victory Financial Group, Inc. | Metairie, LA 70009 | Oil & Gas Operator | Sep 2002 |
| 633 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Feb 2025 |
| 634 | Vista Resources LLC | Teague, TX 75860 | Oil & Gas Operator | May 2025 |
| 635 | Volvo Petroleum, Inc. | | Oil & Gas Operator | Jul 1984 |
| 636 | W. H. Hunt | | Oil & Gas Operator | Jan 1984 |
| 637 | W. L. Estis | | Oil & Gas Operator | Dec 1999 |
| 638 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | May 2025 |
| 639 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 640 | Walter Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 641 | Wapiti Operating, LLC | Houston, TX 77043 | Oil & Gas Operator | May 2025 |
| 642 | Warhorse Oil & Gas, LLC | | Oil & Gas Operator | Dec 2018 |
| 643 | Warwick Oil Corp. | | Oil & Gas Operator | Mar 1990 |
| 644 | Watson Oil Corporation | | Oil & Gas Operator | Jun 1981 |
| 645 | Wayman W. Buchanan | | Oil & Gas Operator | Feb 1986 |
| 646 | Weaver Oil & Gas Corporation | | Oil & Gas Operator | Dec 1984 |
| 647 | Wentworth Production Company | | Oil & Gas Operator | Aug 1985 |
| 648 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 649 | Westport Oil And Gas Company Inc | Denver, CO 80202 | Oil & Gas Operator | Feb 2002 |
| 650 | White Deer Production Co. Inc. | | Oil Operator | Jan 1999 |
| 651 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | May 2025 |
| 652 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 653 | Whittier Operating Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2007 |
| 654 | Will Haristy, Jr. | | Oil & Gas Operator | Nov 2024 |
| 655 | Williams Exploration Company | | Oil & Gas Operator | Dec 1986 |
| 656 | Winchester Production Company | Shreveport, LA 71129 | Oil & Gas Operator | Nov 2008 |
| 657 | Wintershall Corporation | | Oil & Gas Operator | Oct 1989 |
| 658 | Wintershall Oil & Gas Co | | Oil & Gas Operator | Feb 1980 |
| 659 | Wle, Inc. | | Oil & Gas Operator | Feb 2012 |
| 660 | WM. H. Kenny Consultants, LTD. | | Oil & Gas Operator | Nov 1991 |
| 661 | WM. T. Burton Industries, Inc. | | Oil & Gas Operator | Apr 1988 |
| 662 | Woodbine Petroleum, Inc. | Dallas, TX 75204 | Oil & Gas Operator | Aug 2003 |
| 663 | Zachry Exploration, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | May 2025 |
| 664 | Zachry Exploration, LLC | San Antonio, TX 78224 | Oil & Gas Operator | May 2025 |
| 665 | Zadeck Energy Group Inc | | Oil & Gas Operator | Dec 2011 |