| 501 | Sun Texas Company | | Oil & Gas Operator | Jun 1981 |
| 502 | Sunburst, Inc. | Wheat Ridge, CO 80033 | Oil & Gas Operator | Dec 2025 |
| 503 | Superior - Austral | | Oil & Gas Operator | Mar 1978 |
| 504 | Superior Oil Co. | Denver, CO 80217-5444 | Oil & Gas Operator | Feb 2001 |
| 505 | Sutton Joint Account | | Oil Operator | Mar 1988 |
| 506 | Swift Energy Company | Houston, TX 77060 | Oil & Gas Operator | Mar 2021 |
| 507 | Swift Energy Operating, LLC | Houston, TX 77079 | Oil & Gas Operator | Jun 2017 |
| 508 | T & F Oil Company, LLC | | Oil Operator | Oct 2011 |
| 509 | T, F & B Oil Company, LLC | | Oil Operator | Jan 2013 |
| 510 | Tarpon Oil Of Texas | | Oil & Gas Operator | Aug 1994 |
| 511 | Taurus Petr-Fieldcrest Petr | | Oil & Gas Operator | Apr 1989 |
| 512 | Taylor Energy Co. | | Oil & Gas Operator | May 1991 |
| 513 | Team Operating, L.L.C. | Pinehurst, TX 77362 | Oil & Gas Operator | Feb 2026 |
| 514 | Tee Operating Company | | Oil & Gas Operator | Jun 1989 |
| 515 | Tempest Oil Company, Inc. | | Oil & Gas Operator | Jul 1978 |
| 516 | Templeton Energy Inc | | Oil & Gas Operator | Jul 1987 |
| 517 | Tenneco Ventures Corporation | | Oil & Gas Operator | Feb 1996 |
| 518 | Tennessee Gas Pipeline Company | | Oil & Gas Operator | Dec 2011 |
| 519 | Terra Resources, Inc. | Casper, WY 82601 | Oil & Gas Operator | Jun 1990 |
| 520 | Terrier Oil Company | | Oil & Gas Operator | Feb 2015 |
| 521 | Texaco E & P Inc. | Houston, TX 77099 | Oil & Gas Operator | Feb 2026 |
| 522 | Texaco Inc | Kingfisher, OK 73750 | Oil & Gas Operator | Dec 2017 |
| 523 | Texaco Inc & A.C. Glassell Jr | | Oil & Gas Operator | Aug 1980 |
| 524 | Texas Crude, Inc. | Houston, TX 77256 | Oil & Gas Operator | Oct 1995 |
| 525 | Texas Crude-Wainoco-Hilliard | | Oil & Gas Operator | Jul 1978 |
| 526 | Texas Eastern Skyline Oil Co. | | Oil & Gas Operator | Jan 1987 |
| 527 | Texas Eastern Transm. Corp. | | Oil & Gas Operator | Dec 2002 |
| 528 | Texas Ind. Exploration, Inc. | | Oil & Gas Operator | Oct 2001 |
| 529 | Texas Meridian Res. Expl., Inc. | Houston, TX 77079 | Oil & Gas Operator | Jun 1998 |
| 530 | Texas Pacific Oil Co. | | Oil & Gas Operator | Dec 1980 |
| 531 | Texas Petroleum Investment Company | Houston, TX 77057 | Oil & Gas Operator | Feb 2026 |
| 532 | TGX Corporation | Houston, TX 77002 | Oil & Gas Operator | Sep 2004 |
| 533 | Tharp Operating Company | Houston, TX 77070 | Oil & Gas Operator | Nov 2014 |
| 534 | The Ballard & Cordell Corp | | Oil & Gas Operator | Feb 1982 |
| 535 | The Exploration Co. Of La, Inc | | Oil & Gas Operator | Nov 1987 |
| 536 | The Meridian Res. & Exp. LLC | | Oil & Gas Operator | Sep 2010 |
| 537 | The Meridian Resource & Exp Co | | Oil & Gas Operator | Dec 2000 |
| 538 | The Stone Oil Corporation | | Oil & Gas Operator | May 1985 |
| 539 | The Superior Oil Co - Tesoro | | Oil & Gas Operator | Apr 1986 |
| 540 | The WM G Helis Company, L.L.C. | | Oil & Gas Operator | Nov 2003 |
| 541 | Thomas C. Hoffpauir | | Oil & Gas Operator | Mar 1991 |
| 542 | Thomas C. Hoffpauir, Inc. | | Oil & Gas Operator | Jan 1981 |
| 543 | Thrall Texas Oil, LLC | | Oil & Gas Operator | Jan 2025 |
| 544 | Toce Energy, L.L.C. | | Oil & Gas Operator | Dec 2017 |
| 545 | Todd Oil Corp. Of La. Inc. | | Oil & Gas Operator | Jul 2000 |
| 546 | Tom Brown Inc | Denver, CO 80202 | Oil & Gas Operator | Dec 2004 |
| 547 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 548 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |
| 549 | Touchstone Properties, Inc. | | Oil Operator | Mar 1988 |
| 550 | Transcontinental Gas P/L Corp. | | Oil & Gas Operator | Dec 2009 |
| 551 | Transcontinental Oil Corp. | | Oil & Gas Operator | Sep 1985 |
| 552 | Transworld Expl. & Prod., Inc. | | Oil & Gas Operator | Mar 2004 |
| 553 | Tri Investment Company | | Oil Operator | Mar 1980 |
| 554 | Tricentrol Resources Inc | Englewood, CO 80111 | Oil & Gas Operator | Jun 1984 |
| 555 | Tripower Resources, Inc. | Ardmore, OK 73402 | Oil & Gas Operator | Mar 2020 |
| 556 | Triumph Energy Inc | Lafayette, LA 70505 | Oil & Gas Operator | Nov 2015 |
| 557 | Txo Production Corp. | Ganado, TX 77962 | Oil & Gas Operator | Aug 2022 |
| 558 | TXP Operating Co. | | Oil & Gas Operator | Jul 1992 |
| 559 | U S Exploraton Liq Trust | | Oil & Gas Operator | Oct 1994 |
| 560 | U.S. Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 561 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 562 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 563 | Union Expl. Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 564 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 565 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 566 | Union Texas Petroleum Corp | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 567 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Feb 2026 |
| 568 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 569 | United World Energy Corporation | | Oil & Gas Operator | Dec 2024 |
| 570 | Universal Drilling Company | Denver, CO 80203 | Oil & Gas Operator | Sep 2003 |
| 571 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 572 | Usoil Corporation | | Oil & Gas Operator | Nov 1998 |
| 573 | Vale Petroleum Corporation | Houston, TX 77042 | Gas Operator | Jan 1995 |
| 574 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Sep 2025 |
| 575 | Vermilion Bay Land Co. | | Oil & Gas Operator | Dec 1994 |
| 576 | Vernon E. Faulconer | | Oil & Gas Operator | Dec 1996 |
| 577 | Vernon E. Faulconer, Inc. | Tyler, TX 75711 | Oil & Gas Operator | Dec 2024 |
| 578 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |
| 579 | W & T Oil Properties, Inc. | | Oil & Gas Operator | Nov 1989 |
| 580 | W&T Offshore, Inc. | Houston, TX 77057 | Oil & Gas Operator | Feb 2026 |
| 581 | W. B. McCarter, Jr., Inc. | | Oil & Gas Operator | Dec 1995 |
| 582 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 2026 |
| 583 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 584 | Wallace Operating Company | | Oil & Gas Operator | Sep 1986 |
| 585 | Walter Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 586 | Warhorse Oil & Gas, LLC | | Oil & Gas Operator | Dec 2018 |
| 587 | Warwick Oil & Gas, Inc. | Houston, TX 77098 | Oil & Gas Operator | Feb 1993 |
| 588 | Watson Oil Corporation | | Oil & Gas Operator | Jun 1981 |
| 589 | WCC Energy Group LLC | | Oil & Gas Operator | Dec 2024 |
| 590 | Weaver Exploration Company | | Oil & Gas Operator | Jun 1991 |
| 591 | Weaver Oil & Gas Corporation | | Oil & Gas Operator | Dec 1984 |
| 592 | Westland Oil Development Corp. | Conroe, TX 77305 | Oil & Gas Operator | Mar 2008 |
| 593 | Westport Oil And Gas Company Inc | Denver, CO 80202 | Oil & Gas Operator | Feb 2002 |
| 594 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Feb 2026 |
| 595 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 596 | Whitton Company, Inc. | | Oil & Gas Operator | Jul 2020 |
| 597 | Wilcox Operating Corporation | Shreveport, LA 71115 | Oil & Gas Operator | Feb 2026 |
| 598 | Will-Drill Production Co., Inc. | Shreveport, LA 71105 | Oil & Gas Operator | Feb 2026 |
| 599 | William Lagnion | | Oil & Gas Operator | Aug 1998 |
| 600 | Williams Exploration Company | | Oil & Gas Operator | Dec 1986 |