| 501 | Texas Eastern Transm. Corp. | | Oil & Gas Operator | Dec 2002 |
| 502 | Texas Energy & Environmental Inc | Houston, TX 77269 | Oil & Gas Operator | Oct 1998 |
| 503 | Texas Gas Exploration Corp. | | Oil & Gas Operator | Nov 1986 |
| 504 | Texas Gas Transmission Corp. | | Oil Operator | Aug 2003 |
| 505 | Texas Meridian Res. Expl., Inc. | Houston, TX 77079 | Oil & Gas Operator | Jun 1998 |
| 506 | Texas Pacific Oil Co. | | Oil & Gas Operator | Dec 1980 |
| 507 | Texas Petroleum Investment Company | Houston, TX 77057 | Oil & Gas Operator | Feb 2026 |
| 508 | Texoil Company | | Oil & Gas Operator | Dec 2000 |
| 509 | The Meridian Res. & Exp. LLC | | Oil & Gas Operator | Sep 2010 |
| 510 | The Meridian Resource & Exp Co | | Oil & Gas Operator | Dec 2000 |
| 511 | The Stone Oil Corporation | | Oil & Gas Operator | May 1985 |
| 512 | The Stone Petro Corp-Toce Oil | | Oil & Gas Operator | Oct 1984 |
| 513 | The Superior Oc WM Scully Etal | | Oil & Gas Operator | Apr 1986 |
| 514 | Tillman A. Rousse | | Oil Operator | Jan 1990 |
| 515 | Tillman A. Rousse, Inc. | | Oil Operator | Apr 2001 |
| 516 | Tipco | Shreveport, LA 71104-3047 | Oil & Gas Operator | May 1988 |
| 517 | Toce Oil Company | | Oil & Gas Operator | Dec 2014 |
| 518 | Tola Production Company | Dallas, TX 75367 | Oil & Gas Operator | Feb 2026 |
| 519 | Tolar Corporation | | Oil & Gas Operator | Sep 1999 |
| 520 | Tolar Energy, L.L.C. | | Oil & Gas Operator | Dec 2001 |
| 521 | Tom Brown Inc | Denver, CO 80202 | Oil & Gas Operator | Dec 2004 |
| 522 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 523 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |
| 524 | Tradition Resources Oper, LLC | Houston, TX 77002 | Oil & Gas Operator | Jul 2017 |
| 525 | Trafalgar House Oil & Gas Inc | Houston, TX 77002-7346 | Oil & Gas Operator | Jan 1992 |
| 526 | Trans Ocean Oil, Inc. | | Oil & Gas Operator | Sep 1980 |
| 527 | Transfuel Resources Co | Houston, TX 77215 | Oil & Gas Operator | Aug 2013 |
| 528 | Trigon Exploration, Inc. | | Oil & Gas Operator | Jan 1999 |
| 529 | Triton Oil & Gas Corp. | Houston, TX 77002 | Oil & Gas Operator | Nov 2014 |
| 530 | Triumph Energy Inc | Lafayette, LA 70505 | Oil & Gas Operator | Nov 2015 |
| 531 | TXP Operating Co. | | Oil & Gas Operator | Jul 1992 |
| 532 | U S Liquids Of La., L.P. | | Oil Operator | Apr 2014 |
| 533 | U. D. Man, Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Feb 2026 |
| 534 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 535 | Ultramar Production Company | | Oil & Gas Operator | Dec 1991 |
| 536 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 537 | Union Expl. Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 538 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 539 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 540 | Union Texas Petroleum Corp | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 541 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 542 | United Operators, Inc. | | Oil Operator | Sep 1999 |
| 543 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 544 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Feb 2026 |
| 545 | Us Liquids Of La, LTD | | Oil Operator | Jul 2002 |
| 546 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Jan 2026 |
| 547 | Vaughn Petroleum, Inc. | Dallas, TX 75219 | Oil & Gas Operator | May 2004 |
| 548 | Vermillion Energy & Dev. Corp. | | Oil & Gas Operator | Jul 1991 |
| 549 | Vernon E. Faulconer | | Oil & Gas Operator | Dec 1996 |
| 550 | Vernon E. Faulconer, Inc. | Tyler, TX 75711 | Oil & Gas Operator | Dec 2024 |
| 551 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |
| 552 | W&T Offshore, Inc. | Houston, TX 77057 | Oil & Gas Operator | Feb 2026 |
| 553 | W. L. Estis | | Oil & Gas Operator | Dec 1999 |
| 554 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 2026 |
| 555 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 556 | Walter Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 557 | Wayman W. Buchanan | | Oil & Gas Operator | Feb 1986 |
| 558 | Westar Energy, Inc. | Midland, TX 79705 | Oil & Gas Operator | Mar 2008 |
| 559 | White Marlin Operating Company, LLC | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 560 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | Feb 2026 |
| 561 | Whitewing & Whitewing Oil LLC | | Oil & Gas Operator | May 2004 |
| 562 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 563 | Whittier Operating Inc. | Houston, TX 77002 | Oil & Gas Operator | May 2007 |
| 564 | Williams Exploration Company | | Oil & Gas Operator | Dec 1986 |
| 565 | Williams-Cody, Inc. | Houston, TX 77060 | Oil & Gas Operator | May 1994 |
| 566 | Workover One, Inc. | | Oil & Gas Operator | Jul 1989 |
| 567 | WRT Energy Corporation | Oklahoma City, OK 73118 | Oil & Gas Operator | May 1998 |
| 568 | Wylee Petroleum Corporation | | Oil & Gas Operator | Dec 1984 |
| 569 | Xplor Energy Operating Co. | Houston, TX 77079 | Oil & Gas Operator | Jan 2012 |
| 570 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Feb 2026 |
| 571 | Yuma E & P Company, Inc. | Houston, TX 77027 | Oil & Gas Operator | Feb 2026 |
| 572 | Z C Ambrose-G L Blaxton, Jr. | | Oil & Gas Operator | Apr 1983 |
| 573 | Zeit Exploration Co., Inc. | | Oil & Gas Operator | May 1994 |