| 501 | Rme Petroleum Company | Houston, TX 77251 | Oil & Gas Operator | Nov 2016 |
| 502 | Rochelle Oil & Gas | Gillette, WY 82717 | Oil & Gas Operator | Mar 2024 |
| 503 | Rock Creek Resources LLC | Englewood, CO 80112 | Oil & Gas Operator | Dec 2021 |
| 504 | Rock Oil Corporation | Lawrence, KS 66046 | Oil Operator | Oct 2004 |
| 505 | Rockies Resources Holdings LLC | Lakewood, CO 80228 | Oil & Gas Operator | Jan 2026 |
| 506 | Rocky Mountain Gas Inc | Sheridan, WY 82801 | Gas Operator | Nov 2009 |
| 507 | Roemer Oil Company | Denver, CO 80202 | Oil & Gas Operator | Nov 1998 |
| 508 | Roff Operating Company LLC | Houston, TX 77002 | Oil & Gas Operator | Mar 2026 |
| 509 | Royal Resources Exploration | | Oil & Gas Operator | Mar 1984 |
| 510 | Ruby Drilling Company Inc | Gillette, WY 82718 | Oil Operator | Oct 2007 |
| 511 | Sabine Corporation | Oklahoma City, OK 73116 | Oil & Gas Operator | Jul 1996 |
| 512 | Sabine Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2026 |
| 513 | Saga Petroleum LLC Of Colorado | Norman, OK 73072 | Oil & Gas Operator | Mar 2026 |
| 514 | Sage Butte PRB Operating, LLC | Denver, CO 80202 | Oil & Gas Operator | Dec 2025 |
| 515 | Samedan Oil Corporation | Houston, TX 77067 | Oil & Gas Operator | Dec 2019 |
| 516 | Samson Oil & Gas USA Inc | Denver, CO 80202 | Oil & Gas Operator | Jan 2026 |
| 517 | Samson Resources Company LLC | Denver, CO 80202 | Oil & Gas Operator | Feb 2021 |
| 518 | San Marco Petroleum Inc | Denver, CO 80293 | Oil & Gas Operator | Dec 2025 |
| 519 | Sands Oil Company Inc | Billings, MT 59103 | Oil & Gas Operator | Dec 2025 |
| 520 | Santa Rosa Petroleum LLC | Recluse, WY 82725 | Oil & Gas Operator | Nov 2025 |
| 521 | Scana Petroleum Resources Inc | Houston, TX 77002 | Oil & Gas Operator | Jun 2013 |
| 522 | Schmid Properties, Inc. | Hico, TX 76457 | Oil & Gas Operator | Mar 2026 |
| 523 | Seagull Energy E & P Inc | Houston, TX 77002 | Oil & Gas Operator | Jan 2015 |
| 524 | Seer Operating LLC | Sheridan, WY 82801 | Oil & Gas Operator | Oct 2016 |
| 525 | Seguro Oil & Gas Inc | | Oil Operator | Jul 1992 |
| 526 | Seven Sisters Oil & Gas LLC | Casper, WY 82602 | Oil & Gas Operator | Jan 2022 |
| 527 | Shar Alan Oil Company | | Oil & Gas Operator | Oct 2005 |
| 528 | Sharkey Well Service Inc | | Oil Operator | Dec 2023 |
| 529 | Shenandoah Energy Inc | Denver, CO 80265-1050 | Oil & Gas Operator | Dec 2014 |
| 530 | Sheridan Production Company, LLC | Houston, TX 77056 | Oil & Gas Operator | Dec 2025 |
| 531 | Siegfried R H Inc | Tulsa, OK 74104 | Oil & Gas Operator | Mar 2008 |
| 532 | Simasko Production Co | Denver, CO 80204 | Oil & Gas Operator | Nov 1997 |
| 533 | Six Bar Oil LLC | Pine Haven, WY 82721 | Oil & Gas Operator | Jan 2026 |
| 534 | Skinner Oil & Gas LLC | Gillette, WY 82717 | Oil & Gas Operator | Jan 2024 |
| 535 | Skull Creek A LLC | Douglas, WY 82633 | Oil & Gas Operator | Jan 2026 |
| 536 | Skyline Oil Company | Salt Lake City, UT 84111 | Oil & Gas Operator | Jan 1987 |
| 537 | Slaughter J M Oil Company | Fort Worth, TX 76116 | Oil & Gas Operator | Jan 2001 |
| 538 | Slawson Exploration Company Inc | Oklahoma City, OK 73102 | Oil & Gas Operator | Mar 2026 |
| 539 | SM Energy Company | Midland, TX 79707 | Oil & Gas Operator | Mar 2026 |
| 540 | Smith Conley P Operating Co | Eglewood, CO 80112-3640 | Oil & Gas Operator | Jun 2000 |
| 541 | Smokey Oil Company Inc | Casper, WY 82601 | Oil & Gas Operator | Dec 1996 |
| 542 | Snowy Owl LLC | Gillette, WY 82717 | Oil & Gas Operator | Jan 2026 |
| 543 | Snyder Oil Corporation | Houston, TX 77024 | Oil & Gas Operator | Mar 2008 |
| 544 | Sonat Exploration Co. | Houston, TX 77251 | Oil & Gas Operator | Dec 2021 |
| 545 | South Coast Oil Corporation | Boulder, CO 80302 | Oil & Gas Operator | Oct 2015 |
| 546 | South Pass Petroleum Inc | Casper, WY 82601 | Oil & Gas Operator | Jan 2026 |
| 547 | Southland Royalty Company | Houston, TX 77210 | Oil & Gas Operator | Sep 2011 |
| 548 | Southwestern Energy Prod Co | Houston, TX 77032 | Oil & Gas Operator | Jun 2015 |
| 549 | Southwestern Production Corporation | Lakewood, CO 80228 | Oil & Gas Operator | Jan 2026 |
| 550 | Spirit Energy Inc | Edmond, OK 73034 | Oil & Gas Operator | Apr 1999 |
| 551 | St. Mary Operating Company | Denver, CO 80203 | Oil & Gas Operator | Mar 2019 |
| 552 | Stag Oil Producers Inc | Midland, TX 79701 | Oil & Gas Operator | Jan 1998 |
| 553 | Star Resources LLC | Englewood, CO 80155-5185 | Oil & Gas Operator | Dec 2013 |
| 554 | States Exploration Inc | | Oil Operator | Jul 1985 |
| 555 | Statex Petroleum Inc | Dallas, TX 75229 | Oil & Gas Operator | Dec 2000 |
| 556 | Steamboat Oil And Gas LLC | Gillette, WY 82717 | Oil Operator | Jan 2026 |
| 557 | Stellar Oil Company | Arvada, CO 80006 | Oil & Gas Operator | Dec 1998 |
| 558 | Stephens Production Company | The Woodlands, TX 77381 | Oil & Gas Operator | Jan 2026 |
| 559 | Sterling Energy Corporation | Denver, CO 80202 | Oil & Gas Operator | Sep 1995 |
| 560 | Stewart Petroleum Corporation | Greenwood VIllage, CO 80111 | Oil & Gas Operator | Dec 2023 |
| 561 | Stone & Wolf LLC | Sheridan, WY 82801 | Oil & Gas Operator | Dec 2006 |
| 562 | Stone Petroleum Corporation | | Oil & Gas Operator | Dec 1996 |
| 563 | Storm Cat Energy USA Operating Corp | Denver, CO 80202 | Gas Operator | Jun 2017 |
| 564 | Stovall Oil Company | Casper, WY 82602 | Oil & Gas Operator | Aug 1998 |
| 565 | Stroud Petroleum, Inc. | Shreveport, LA 71162 | Oil & Gas Operator | Mar 2026 |
| 566 | Summit Gas Resources Inc | Sheridan, WY 82801 | Gas Operator | Dec 2023 |
| 567 | Suncor Energy Natural Gas America Inc | Greenwood VIllage, CO 80111 | Gas Operator | Feb 2010 |
| 568 | Sundance Oil Exploration Co | | Oil Operator | Mar 1986 |
| 569 | Sunshine Valley Petroleum | Casper, WY 82605 | Oil & Gas Operator | Jan 2026 |
| 570 | Swenco-Western Inc | Houston, TX 77060 | Oil & Gas Operator | Jan 1997 |
| 571 | Swepi LP | Houston, TX 77079 | Oil & Gas Operator | Jul 2020 |
| 572 | Swift Energy Company | Houston, TX 77060 | Oil & Gas Operator | Mar 2021 |
| 573 | T2 Operating Corporation | Denver, CO 80202 | Oil & Gas Operator | Mar 2026 |
| 574 | Taqa USA, Inc. | Centennial, CO 80111 | Oil & Gas Operator | Jul 2020 |
| 575 | Tbi Exploration Inc | Englewood, CO 801556525 | Oil & Gas Operator | Jun 2011 |
| 576 | Team Operating, L.L.C. | Pinehurst, TX 77362 | Oil & Gas Operator | Mar 2026 |
| 577 | Temagami Oil & Gas LTD | | Oil & Gas Operator | May 2007 |
| 578 | Tenneco Oil Company | Oklahoma City, OK 73125 | Oil & Gas Operator | Dec 2025 |
| 579 | Territory Resources LLC | Stillwater, OK 74074-1869 | Oil & Gas Operator | Feb 2026 |
| 580 | Terry Production Co | Stroud, OK 74079-0475 | Oil & Gas Operator | Aug 2008 |
| 581 | Texaco Exploration & Prod | Midland, TX 79702 | Oil & Gas Operator | Aug 2002 |
| 582 | Texakota | | Oil & Gas Operator | Mar 1995 |
| 583 | Texas General Petroleum Corp | | Oil & Gas Operator | Aug 1984 |
| 584 | Texas Oil & Gas Corporation | Dallas, TX 75201 | Oil & Gas Operator | Feb 2001 |
| 585 | The Termo Company | Long Beach, CA 90801 | Oil & Gas Operator | Jan 2026 |
| 586 | Thomas Operating Company Inc | Greeley, CO 80634 | Oil & Gas Operator | Aug 2008 |
| 587 | Three Forks Resources, LLC | Wheat Ridge, CO 80033 | Oil & Gas Operator | Mar 2026 |
| 588 | Timberline Energy Inc | Franklin, PA 16323-0269 | Oil & Gas Operator | Dec 2025 |
| 589 | Timberline Production Company LLC | Casper, WY 82601 | Oil & Gas Operator | Oct 2020 |
| 590 | Tindall Operating Company | Englewood, CO 80112 | Oil & Gas Operator | Jan 2025 |
| 591 | Titan Exploration LLC | Denver, CO 80202 | Oil & Gas Operator | Jan 2026 |
| 592 | Tonka Oil & Gas Production Inc | Buffalo, WY 82834 | Oil & Gas Operator | Sep 1999 |
| 593 | Torch E & P Company | Houston, TX 77010 | Oil & Gas Operator | Jan 2015 |
| 594 | Torch Oil & Gas Company | Houston, TX 77010 | Oil & Gas Operator | Aug 1997 |
| 595 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 596 | Total Petroleum Inc | Houston, TX 77210 | Oil & Gas Operator | Feb 1998 |
| 597 | TR Operating LLC | Graham, TX 76450 | Oil Operator | Dec 2025 |
| 598 | Transcontinental Oil Corp. | | Oil & Gas Operator | Sep 1985 |
| 599 | Transhorizon Energy Inc | Cheyenne, WY 82003 | Oil & Gas Operator | Jul 2023 |
| 600 | Trend Exploration I LLC | Midland, TX 79701 | Oil & Gas Operator | May 2011 |