| 501 | Sandefer Petroleum Co. | | Oil & Gas Operator | Apr 1994 |
| 502 | Santa Fe Energy Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Mar 2008 |
| 503 | Seahawk Oil & Gas Company | Dallas, TX 75379 | Oil & Gas Operator | Aug 2007 |
| 504 | Sealexco | | Oil & Gas Operator | Jun 1992 |
| 505 | Senior G&A Operating Co Inc | | Oil & Gas Operator | Nov 1991 |
| 506 | Shale Energy International, LLC | | Oil & Gas Operator | Nov 2024 |
| 507 | Shelf Energy, LLC | | Oil & Gas Operator | Dec 2024 |
| 508 | Shell Offshore Inc. | New Orleans, LA 70161 | Oil & Gas Operator | Jan 2008 |
| 509 | Shell Oil Co. | Houston, TX 77001 | Oil & Gas Operator | Jun 1985 |
| 510 | Shell Western E&P Inc. | Houston, TX 77001 | Oil & Gas Operator | May 2011 |
| 511 | Shore Oil Company | | Oil & Gas Operator | May 1998 |
| 512 | Shoreline Southeast LLC | | Oil & Gas Operator | Jun 2017 |
| 513 | Shuteston Oil & Gas | | Oil & Gas Operator | Sep 1997 |
| 514 | Signal Petroleum | | Oil & Gas Operator | Jul 1980 |
| 515 | Smith Production Co. | Wichita Falls, TX 76308 | Oil & Gas Operator | Dec 2025 |
| 516 | Snyder Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Mar 2015 |
| 517 | Snyder Oil Corporation | Houston, TX 77024 | Oil & Gas Operator | Mar 2008 |
| 518 | Sohio Petroleum Co. | Casper, WY 82602 | Oil & Gas Operator | Apr 1986 |
| 519 | Solatex | | Oil & Gas Operator | Oct 1978 |
| 520 | Sonat Exploration Co. | Houston, TX 77251 | Oil & Gas Operator | Dec 2021 |
| 521 | Sonora Producing, Inc. | | Oil & Gas Operator | May 2006 |
| 522 | Southport Exploration Inc | Tulsa, OK 74103-4015 | Oil & Gas Operator | Nov 1998 |
| 523 | Southwest Oil Properties, Inc. | | Oil & Gas Operator | Feb 1996 |
| 524 | Southwest Rig Service | | Oil & Gas Operator | Nov 1998 |
| 525 | Southwestern Energy Prod Co | Houston, TX 77032 | Oil & Gas Operator | Jun 2015 |
| 526 | Square Mile Energy, L.L.C. | Houston, TX 77057 | Oil & Gas Operator | Dec 2025 |
| 527 | SRP Production Corp. | | Oil & Gas Operator | Nov 1997 |
| 528 | St. Mary Energy Company | Houston, TX 77079 | Oil & Gas Operator | Aug 2008 |
| 529 | St. Mary Land & Exploration Co | Denver, CO 80201 | Oil & Gas Operator | Jun 2010 |
| 530 | St. Mary Operating Company | Denver, CO 80203 | Oil & Gas Operator | Mar 2019 |
| 531 | Stone Energy Corporation | Denver, CO 80202-2828 | Oil & Gas Operator | Oct 2014 |
| 532 | Stone Petroleum Corporation | | Oil & Gas Operator | Dec 1996 |
| 533 | Strata Energy, Inc. | | Oil & Gas Operator | Sep 1983 |
| 534 | Stratco Operating Co Inc | Austin, TX 78701 | Oil & Gas Operator | Dec 2025 |
| 535 | Summit Energy,Inc | Littleton, CO 80127 | Oil & Gas Operator | Aug 2013 |
| 536 | Summit Overseas Expl., Inc. | Denver, CO 80226 | Oil & Gas Operator | Apr 2007 |
| 537 | Sun Exploration And Production Co | | Oil & Gas Operator | Jan 1990 |
| 538 | Sunchase Exploration, Inc. | | Oil & Gas Operator | Oct 1997 |
| 539 | Superior Oil Co. | Denver, CO 80217-5444 | Oil & Gas Operator | Feb 2001 |
| 540 | Swift Energy Company | Houston, TX 77060 | Oil & Gas Operator | Mar 2021 |
| 541 | Talos Third Coast LLC | | Oil & Gas Operator | Dec 2024 |
| 542 | Targa Midstream Services LLC | Houston, TX 77002 | Oil Operator | Mar 2023 |
| 543 | TD & Associates, Inc. | | Oil & Gas Operator | Jun 1998 |
| 544 | Teal Petroleum Co. | | Oil & Gas Operator | Sep 1978 |
| 545 | Tecpetrol Operating LLC | Houston, TX 77027 | Oil & Gas Operator | Dec 2015 |
| 546 | Tee Operating Company | | Oil & Gas Operator | Jun 1989 |
| 547 | Temex Energy Inc | Oklahoma City, OK 73101 | Oil & Gas Operator | Feb 2002 |
| 548 | Tenneco Oil Company | Oklahoma City, OK 73125 | Oil & Gas Operator | Sep 2025 |
| 549 | Tensas Exploraton & Production Co LLC | | Oil & Gas Operator | Nov 2009 |
| 550 | Tepco Resources, Inc. | Houston, TX 77027 | Oil & Gas Operator | Sep 2004 |
| 551 | Terra Resources, Inc. | Casper, WY 82601 | Oil & Gas Operator | Jun 1990 |
| 552 | Tesla Resources, Inc. | | Oil & Gas Operator | Aug 1996 |
| 553 | Tex/Con Oil & Gas Company | Houston, TX 77074 | Oil & Gas Operator | Feb 2001 |
| 554 | Texaco E & P Inc. | Houston, TX 77099 | Oil & Gas Operator | Dec 2025 |
| 555 | Texaco Inc | Kingfisher, OK 73750 | Oil & Gas Operator | Dec 2017 |
| 556 | Texaco Producing Inc. | Rock Springs, WY 82901 | Oil & Gas Operator | Dec 2000 |
| 557 | Texas Crude Oil Co. Et Al | | Oil & Gas Operator | May 1992 |
| 558 | Texas Crude Operator, Inc. | Houston, TX 77098 | Oil & Gas Operator | Aug 2017 |
| 559 | Texas Crude, Inc. | Houston, TX 77256 | Oil & Gas Operator | Oct 1995 |
| 560 | Texas Gas Exploration Corp. | | Oil & Gas Operator | Nov 1986 |
| 561 | Texas Oil & Gas Corporation | Dallas, TX 75201 | Oil & Gas Operator | Feb 2001 |
| 562 | Texas Petroleum Investment Company | Houston, TX 77057 | Oil & Gas Operator | Dec 2025 |
| 563 | The Ballard & Cordell Corp | | Oil & Gas Operator | Feb 1982 |
| 564 | The Exploration Co. Of La, Inc | | Oil & Gas Operator | Nov 1987 |
| 565 | The George R Brown Partnership | | Oil & Gas Operator | Jun 1992 |
| 566 | The Meridian Res. & Exp. LLC | | Oil & Gas Operator | Sep 2010 |
| 567 | The Meridian Resource & Exp Co | | Oil & Gas Operator | Dec 2000 |
| 568 | The Southern Louisiana Expl. Company LLC | | Oil & Gas Operator | Nov 2024 |
| 569 | The Stone Oil Corporation | | Oil & Gas Operator | May 1985 |
| 570 | The Superior Oil Co & Pel-Tex | | Oil & Gas Operator | Apr 1986 |
| 571 | The Termo Company | Long Beach, CA 90801 | Oil & Gas Operator | Oct 2025 |
| 572 | Toce Energy, L.L.C. | | Oil & Gas Operator | Dec 2017 |
| 573 | Toce Oil Company | | Oil & Gas Operator | Dec 2014 |
| 574 | Tola Production Company | Dallas, TX 75367 | Oil & Gas Operator | Dec 2025 |
| 575 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 576 | Torrid Energy Company | | Oil & Gas Operator | Jun 1988 |
| 577 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |
| 578 | Transcontinental Gas P/L Corp. | | Oil & Gas Operator | Dec 2009 |
| 579 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 580 | Tricentrol Resources Inc | Englewood, CO 80111 | Oil & Gas Operator | Jun 1984 |
| 581 | Trigon Exploration, Inc. | | Oil & Gas Operator | Jan 1999 |
| 582 | Triumph Energy Inc | Lafayette, LA 70505 | Oil & Gas Operator | Nov 2015 |
| 583 | Triumph Energy Inc-P B Berry | | Oil & Gas Operator | Jun 1986 |
| 584 | Trunkline Gas Company | | Oil Operator | Mar 2008 |
| 585 | Txo Production Corp. | Ganado, TX 77962 | Oil & Gas Operator | Aug 2022 |
| 586 | TXP Operating Co. | | Oil & Gas Operator | Jul 1992 |
| 587 | U. S. Operating, Inc. | Dallas, TX 75252 | Oil & Gas Operator | Jul 2025 |
| 588 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 589 | Union Expl. Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 590 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 591 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 592 | Union Texas Petroleum Corp | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 593 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Dec 2025 |
| 594 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 595 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 596 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Dec 2025 |
| 597 | Van Operating, LTD. | Albany, TX 76430 | Oil & Gas Operator | Dec 2025 |
| 598 | Vastar Resources Inc | Houston, TX 77253 | Oil & Gas Operator | Jun 2025 |
| 599 | Vector Minerals Corporation | Aurora, CO 80015 | Oil & Gas Operator | Sep 2025 |
| 600 | Vernon E. Faulconer, Inc. | Tyler, TX 75711 | Oil & Gas Operator | Dec 2024 |