| 501 | Redman Operating Company | Houston, TX 77042 | Oil & Gas Operator | May 2008 |
| 502 | Reliable Prod Service Inc. | | Oil Operator | Mar 2007 |
| 503 | Rental & Fishing Tools, Inc. | | Oil Operator | Dec 2024 |
| 504 | Republic Prod.Co.Of Tex., Inc | | Oil & Gas Operator | Jun 1981 |
| 505 | Resource Securities Corp. | | Oil & Gas Operator | Mar 2005 |
| 506 | Resources Investment Corp | Denver, CO 80202 | Oil & Gas Operator | Sep 2018 |
| 507 | Riceland Petroleum Company | | Oil & Gas Operator | Nov 2024 |
| 508 | Ridgeway Exco, Inc. | San Antonio, TX 78279 | Oil & Gas Operator | Mar 1996 |
| 509 | Rio Bravo Oil Company | The Woodlands, TX 77381 | Oil & Gas Operator | Feb 2002 |
| 510 | Riseden, LTD | | Oil & Gas Operator | Nov 1989 |
| 511 | RLP Gulf States, L.L.C. | | Oil & Gas Operator | Apr 2012 |
| 512 | Rockbridge Oil & Gas | Houston, TX 77027 | Oil & Gas Operator | Mar 1990 |
| 513 | Rodessa Operating Company | Corpus Chrsti, TX 78426 | Oil & Gas Operator | Oct 2025 |
| 514 | Ross-A. J. Hodges Ind. | | Oil & Gas Operator | Dec 1980 |
| 515 | Roy M. Teel | | Oil & Gas Operator | Nov 1983 |
| 516 | Rozel Operating Company | | Oil & Gas Operator | Oct 2014 |
| 517 | Ruby Breaux Gotreaux | | Oil Operator | Mar 1981 |
| 518 | Rvo Petroleum Co. | | Oil & Gas Operator | Feb 1982 |
| 519 | Sable Minerals, Inc. | | Oil & Gas Operator | Nov 1993 |
| 520 | Saline Injection Systems Co. | | Oil Operator | Jan 2025 |
| 521 | Samson Contour Energy E&P, LLC | Tulsa, OK 74103 | Oil & Gas Operator | Sep 2017 |
| 522 | Samson Exploration LLC | Tulsa, OK 74101 | Oil & Gas Operator | Aug 2025 |
| 523 | Samson Resources Company | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 524 | Sandefer Petroleum Co. | | Oil & Gas Operator | Apr 1994 |
| 525 | Sante Fe Minerals | | Oil & Gas Operator | Dec 1987 |
| 526 | Scurlock Oil Co | | Oil Operator | May 1982 |
| 527 | Se USA Operating, Inc. | Houston, TX 77002 | Oil & Gas Operator | Dec 2009 |
| 528 | Seaboard Pipe & Equip. Co. | | Oil & Gas Operator | May 1977 |
| 529 | Seagull Operating Co., Inc. | Shreveport, LA 71101 | Oil & Gas Operator | Jan 2025 |
| 530 | Seal Energy Company | | Oil Operator | Dec 2024 |
| 531 | Sealexco | | Oil & Gas Operator | Jun 1992 |
| 532 | Secondary Recovery, Inc. | | Oil & Gas Operator | Dec 1991 |
| 533 | Sevarg Company, Inc. | | Oil & Gas Operator | Feb 2016 |
| 534 | Shale Energy International, LLC | | Oil & Gas Operator | Nov 2024 |
| 535 | Shelf Energy, LLC | | Oil & Gas Operator | Dec 2024 |
| 536 | Shenandoah Oil Corporation | | Oil & Gas Operator | Jun 1979 |
| 537 | Simar Petroleum, LLC | | Oil Operator | Dec 2024 |
| 538 | Simco Oil Company | | Oil Operator | Jul 1990 |
| 539 | Sitwell, Inc. | | Oil Operator | May 2022 |
| 540 | Solatex Resources, LTD | Houston, TX 77257 | Oil & Gas Operator | Oct 2025 |
| 541 | Sonat Exploration Co. | Houston, TX 77251 | Oil & Gas Operator | Dec 2021 |
| 542 | Source Petroleum Inc. | San Antonio, TX 78265 | Oil & Gas Operator | Oct 2025 |
| 543 | South La. Production Co., Inc. | | Oil & Gas Operator | Jun 1982 |
| 544 | Southern Production & Expl Co. | | Oil & Gas Operator | Apr 2008 |
| 545 | Southwest Gas Producing Co Inc | | Oil & Gas Operator | Nov 1994 |
| 546 | Southwest Oil Properties, Inc. | | Oil & Gas Operator | Feb 1996 |
| 547 | Southwestern Energy Prod Co | Houston, TX 77032 | Oil & Gas Operator | Jun 2015 |
| 548 | Speco Oil Company | | Oil & Gas Operator | Feb 1980 |
| 549 | Square Mile Energy, L.L.C. | Houston, TX 77057 | Oil & Gas Operator | Oct 2025 |
| 550 | SRP Production Corp. | | Oil & Gas Operator | Nov 1997 |
| 551 | St. Mary Land & Exploration Co | Denver, CO 80201 | Oil & Gas Operator | Jun 2010 |
| 552 | St. Mary Operating Company | Denver, CO 80203 | Oil & Gas Operator | Mar 2019 |
| 553 | Stone Petroleum Corporation | | Oil & Gas Operator | Dec 1996 |
| 554 | Stratco Operating Co Inc | Austin, TX 78701 | Oil & Gas Operator | Oct 2025 |
| 555 | Sun Exploration-Production Co. | | Oil & Gas Operator | Jan 1990 |
| 556 | Sun Texas Company | | Oil & Gas Operator | Jun 1981 |
| 557 | Sunchase Exploration, Inc. | | Oil & Gas Operator | Oct 1997 |
| 558 | Superior Oil Co. | Denver, CO 80217-5444 | Oil & Gas Operator | Feb 2001 |
| 559 | Swift Energy Company | Houston, TX 77060 | Oil & Gas Operator | Mar 2021 |
| 560 | Synergy Oil & Gas, L.P. | Houston, TX 77024 | Oil & Gas Operator | May 2012 |
| 561 | T & M Gauging | | Oil Operator | Oct 2006 |
| 562 | Tabco Exploration Inc. | New Orleans, LA 70131 | Oil & Gas Operator | Dec 1998 |
| 563 | Tammany Oil & Gas LLC | | Oil & Gas Operator | Feb 2005 |
| 564 | Targa Midstream Services LLC | Houston, TX 77002 | Oil Operator | Mar 2023 |
| 565 | Tarpon Oil Of Texas | | Oil & Gas Operator | Aug 1994 |
| 566 | Taurus Petr-Fieldcrest Petr | | Oil & Gas Operator | Apr 1989 |
| 567 | Taurus Petroleum | | Oil & Gas Operator | Jul 1987 |
| 568 | Tee Operating Company | | Oil & Gas Operator | Jun 1989 |
| 569 | Tellus Operating Group, LLC | | Oil & Gas Operator | Jun 2025 |
| 570 | Tenneco Inc. | | Oil & Gas Operator | Jun 1989 |
| 571 | Terra Resources, Inc. | Casper, WY 82601 | Oil & Gas Operator | Jun 1990 |
| 572 | Terrier Oil Company | | Oil & Gas Operator | Feb 2015 |
| 573 | Tesla Resources, Inc. | | Oil & Gas Operator | Aug 1996 |
| 574 | Texaco E & P Inc | Houston, TX 77099 | Oil & Gas Operator | Oct 2025 |
| 575 | Texaco Producing Inc. | Rock Springs, WY 82901 | Oil & Gas Operator | Dec 2000 |
| 576 | Texas Crude, Inc. | Houston, TX 77256 | Oil & Gas Operator | Oct 1995 |
| 577 | Texas Eastern Transm. Corp. | | Oil & Gas Operator | Dec 2002 |
| 578 | Texas Gas Exploration Corp. | | Oil & Gas Operator | Nov 1986 |
| 579 | Texas Gas Transmission Corp. | | Oil Operator | Aug 2003 |
| 580 | Texas Gas Transmission LLC | Owensboro, KY 42301 | Oil & Gas Operator | Dec 2024 |
| 581 | Texas Meridian Operating Co. Inc | Houston, TX 77079 | Oil & Gas Operator | Oct 1993 |
| 582 | Texas Pacific Oil Company Inc. | | Oil & Gas Operator | Dec 1980 |
| 583 | Texas Petroleum Investment Company | Houston, TX 77057 | Oil & Gas Operator | Oct 2025 |
| 584 | Texasgulf Inc. | Newgulf, TX 77462 | Oil & Gas Operator | Jul 1994 |
| 585 | The Bering Company | | Oil Operator | Jul 1979 |
| 586 | The Petroleum Corp Of Delaware | | Oil & Gas Operator | May 1991 |
| 587 | The Southern Louisiana Expl. Company LLC | | Oil & Gas Operator | Nov 2024 |
| 588 | The Stone Oil Corporation | | Oil & Gas Operator | May 1985 |
| 589 | Thrall Texas Oil, LLC | | Oil & Gas Operator | Jan 2025 |
| 590 | Three D Petroleum LLC | | Oil Operator | Dec 2024 |
| 591 | Three S & T Oil Co., Inc. | | Oil & Gas Operator | May 1985 |
| 592 | Tideland Industries, Inc. | | Oil & Gas Operator | Dec 1989 |
| 593 | Tideway Oil Programs, Inc. | | Oil & Gas Operator | Oct 1980 |
| 594 | Tiger Petroleum | | Oil Operator | Sep 2002 |
| 595 | Tigner Walker | | Oil & Gas Operator | Dec 2021 |
| 596 | Tillman J. McIntyre | | Oil Operator | Dec 1987 |
| 597 | Toce Energy, L.L.C. | | Oil & Gas Operator | Dec 2017 |
| 598 | Torch Energy Services, Inc. | Houston, TX 77010 | Oil & Gas Operator | Sep 2011 |
| 599 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 600 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |