| 501 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 502 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 503 | Union Texas Petroleum Corp | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 504 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 505 | United World Energy Corporation | | Oil & Gas Operator | Dec 2024 |
| 506 | Universal Drilling Company | Denver, CO 80203 | Oil & Gas Operator | Sep 2003 |
| 507 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Jan 2026 |
| 508 | Vast Oil Inc | Fullerton, CA 92832 | Oil & Gas Operator | Mar 2024 |
| 509 | Vermilion Bay Land Co. | | Oil & Gas Operator | Dec 1994 |
| 510 | Vernon E. Faulconer, Inc. | Tyler, TX 75711 | Oil & Gas Operator | Dec 2024 |
| 511 | Vibe Resources LLC | | Oil & Gas Operator | Dec 2024 |
| 512 | Victoria Land & Investment Co. | | Oil & Gas Operator | Jan 1985 |
| 513 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |
| 514 | Vonco Of Mississippi, Inc. | | Oil Operator | Dec 2025 |
| 515 | W B Powers Production Serv. | | Oil Operator | Feb 1991 |
| 516 | W. L. Estis | | Oil & Gas Operator | Dec 1999 |
| 517 | W. L. Puls & T. D. Rush | | Oil & Gas Operator | Dec 1980 |
| 518 | W. T. Waggoner Estate | | Oil & Gas Operator | Dec 1995 |
| 519 | Wagner & Brown | Midland, TX 79702 | Oil & Gas Operator | Aug 2014 |
| 520 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 2026 |
| 521 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 522 | Walker La. Properties | | Oil & Gas Operator | Oct 1990 |
| 523 | Warwick Oil & Gas, Inc. | Houston, TX 77098 | Oil & Gas Operator | Feb 1993 |
| 524 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 525 | Westport Oil And Gas Company Inc | Denver, CO 80202 | Oil & Gas Operator | Feb 2002 |
| 526 | White Marlin Operating Company, LLC | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 527 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Feb 2026 |
| 528 | Whitton Company, Inc. | | Oil & Gas Operator | Jul 2020 |
| 529 | Windrush Operating Company | | Oil & Gas Operator | Jan 2009 |
| 530 | Wiser Oil Co | Denver, CO 80202 | Oil & Gas Operator | Dec 2023 |
| 531 | Wle, Inc. | | Oil & Gas Operator | Feb 2012 |
| 532 | WM. H. Kenny Consultants, LTD. | | Oil & Gas Operator | Nov 1991 |
| 533 | Woodbine Petroleum, Inc. | Dallas, TX 75204 | Oil & Gas Operator | Aug 2003 |
| 534 | Woolf & Magee, Inc. | | Oil & Gas Operator | Oct 1991 |
| 535 | XCL-Louisiana, Inc. | | Oil & Gas Operator | Aug 1993 |
| 536 | Xeric Oil & Gas Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 2014 |
| 537 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Feb 2026 |
| 538 | Yellow Rock, LLC | | Oil & Gas Operator | Dec 2024 |
| 539 | Yuma E & P Company, Inc. | Houston, TX 77027 | Oil & Gas Operator | Feb 2026 |
| 540 | Zachry Exploration, Inc. | San Antonio, TX 78205 | Oil & Gas Operator | Feb 2026 |
| 541 | Zachry Exploration, LLC | San Antonio, TX 78224 | Oil & Gas Operator | Feb 2026 |
| 542 | Zachry Exploration, LTD. | San Antonio, TX 78205 | Oil & Gas Operator | Jan 2009 |
| 543 | Zenergy Inc | Tulsa, OK 74136 | Oil & Gas Operator | Dec 2025 |
| 544 | Zinke & Trumbo, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2007 |
| 545 | Zinn Petroleum Co. | Houston, TX 77024 | Oil & Gas Operator | Nov 2021 |