| 601 | Sundance Oil Exploration Co | | Oil Operator | Mar 1986 |
| 602 | Sunshine Valley Petroleum | Casper, WY 82605 | Oil & Gas Operator | May 2025 |
| 603 | Swenco-Western Inc | Houston, TX 77060 | Oil & Gas Operator | Jan 1997 |
| 604 | Swepi LP | Houston, TX 77079 | Oil & Gas Operator | Jul 2020 |
| 605 | Swift Energy Company | Houston, TX 77060 | Oil & Gas Operator | Mar 2021 |
| 606 | T2 Operating Corporation | Denver, CO 80202 | Oil & Gas Operator | Jul 2025 |
| 607 | Taqa USA, Inc. | Centennial, CO 80111 | Oil & Gas Operator | Jul 2020 |
| 608 | Tbi Exploration Inc | Englewood, CO 801556525 | Oil & Gas Operator | Jun 2011 |
| 609 | Tbi Production Company | Lakewood, CO 80228 | Oil & Gas Operator | Oct 2004 |
| 610 | Team Operating, L.L.C. | Pinehurst, TX 77362 | Oil & Gas Operator | Jul 2025 |
| 611 | Temagami Oil & Gas LTD | | Oil & Gas Operator | May 2007 |
| 612 | Tenneco Oil Company | Oklahoma City, OK 73125 | Oil & Gas Operator | Apr 2025 |
| 613 | Territory Resources LLC | Stillwater, OK 74074-1869 | Oil & Gas Operator | Jun 2025 |
| 614 | Terry Production Co | Stroud, OK 74079-0475 | Oil & Gas Operator | Aug 2008 |
| 615 | Texaco Exploration & Prod | Midland, TX 79702 | Oil & Gas Operator | Aug 2002 |
| 616 | Texakota | | Oil & Gas Operator | Mar 1995 |
| 617 | Texas General Petroleum Corp | | Oil & Gas Operator | Aug 1984 |
| 618 | Texas Oil & Gas Corporation | Dallas, TX 75201 | Oil & Gas Operator | Feb 2001 |
| 619 | The Termo Company | Long Beach, CA 90801 | Oil & Gas Operator | May 2025 |
| 620 | Thomas Operating Company Inc | Greeley, CO 80634 | Oil & Gas Operator | Aug 2008 |
| 621 | Three Forks Resources LLC | Wheat Ridge, CO 80033 | Oil & Gas Operator | Jul 2025 |
| 622 | Timberline Energy Inc | Franklin, PA 16323-0269 | Oil & Gas Operator | Dec 2024 |
| 623 | Timberline Production Company LLC | Casper, WY 82601 | Oil & Gas Operator | Oct 2020 |
| 624 | Tindall Operating Company | Englewood, CO 80112 | Oil & Gas Operator | Jan 2025 |
| 625 | Titan Exploration LLC | Denver, CO 80202 | Oil & Gas Operator | May 2025 |
| 626 | Tonka Oil & Gas Production Inc | Buffalo, WY 82834 | Oil & Gas Operator | Sep 1999 |
| 627 | Torch E & P Company | Houston, TX 77010 | Oil & Gas Operator | Jan 2015 |
| 628 | Torch Oil & Gas Company | Houston, TX 77010 | Oil & Gas Operator | Aug 1997 |
| 629 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 630 | Total Petroleum Inc | Houston, TX 77210 | Oil & Gas Operator | Feb 1998 |
| 631 | TR Operating LLC | Graham, TX 76450 | Oil Operator | Jun 2025 |
| 632 | Transcontinental Oil Corp. | | Oil & Gas Operator | Sep 1985 |
| 633 | Transhorizon Energy Inc | Cheyenne, WY 82003 | Oil & Gas Operator | Jul 2023 |
| 634 | Trend Exploration I LLC | Midland, TX 79701 | Oil & Gas Operator | May 2011 |
| 635 | Tresor Petroleum | | Oil & Gas Operator | Sep 1987 |
| 636 | Triangle J Oil Company | | Oil & Gas Operator | Mar 2007 |
| 637 | Trigg Oil Mining Corporation | | Oil & Gas Operator | Dec 2007 |
| 638 | Trinity Energy Resources Inc | Houston, TX 77079 | Oil & Gas Operator | Aug 2005 |
| 639 | Triple B Energy Inc | Gillette, WY 82716 | Oil Operator | Dec 1999 |
| 640 | Tripower Resources LLC | Ardmore, OK 73402 | Oil & Gas Operator | Jul 2025 |
| 641 | Tripp Oil Company Inc | Houston, TX 77023 | Oil & Gas Operator | Jan 1992 |
| 642 | Trout Kye Jr | | Oil & Gas Operator | Dec 2010 |
| 643 | True Oil LLC | Casper, WY 82602 | Oil & Gas Operator | Jun 2025 |
| 644 | Txo Production Corp. | Ganado, TX 77962 | Oil & Gas Operator | Aug 2022 |
| 645 | U V Industries | | Oil & Gas Operator | Jan 1993 |
| 646 | Underwood Oil & Gas | Casper, WY 82602 | Oil & Gas Operator | Jun 2025 |
| 647 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 648 | Union Texas Petroleum | Houston, TX 77252 | Oil & Gas Operator | Oct 1991 |
| 649 | United Natural Resources Corp | | Oil Operator | Jan 1986 |
| 650 | United Petroleum Corporation | Edgwater, CO 80214 | Oil & Gas Operator | May 1996 |
| 651 | Updike Resources Inc | Newcastle, WY 82701 | Oil & Gas Operator | Jun 1998 |
| 652 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Jul 2025 |
| 653 | USA Exploration & Production LLC | Mills, WY 82644 | Oil & Gas Operator | Sep 2012 |
| 654 | Valero Producing Company | | Oil Operator | Sep 1987 |
| 655 | Valkyrie Operating LLC | Denver, CO 80202 | Oil & Gas Operator | Jun 2025 |
| 656 | Van Norman Pipe And Supply | | Oil & Gas Operator | Mar 2010 |
| 657 | Vast Oil Inc | Fullerton, CA 92832 | Oil & Gas Operator | Mar 2024 |
| 658 | Vecta Oil & Gas LTD | Dallas, TX 75235 | Oil & Gas Operator | May 2025 |
| 659 | Vermilion Energy USA LLC | | Oil & Gas Operator | May 2025 |
| 660 | Vicorp Energy Inc | Denver, CO 80202-4927 | Oil & Gas Operator | Mar 2001 |
| 661 | Viking Resources Corp | Deerfield, OH 44411-0160 | Oil & Gas Operator | Dec 2007 |
| 662 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Apr 2025 |
| 663 | Viola Production Inc | Dallas, TX 75251 | Oil & Gas Operator | Jul 2025 |
| 664 | Wacker Oil Inc | Houston, TX 77002 | Oil & Gas Operator | Aug 1996 |
| 665 | Waggoner-Baldridge Energy | | Oil Operator | Jun 1988 |
| 666 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 667 | Wallway M J | Casper, WY 82601 | Oil & Gas Operator | Jan 1993 |
| 668 | Warren E & P Inc | Dallas, TX 75240 | Oil & Gas Operator | Apr 2025 |
| 669 | Warren Enterprises Inc | Gillette, WY 82718 | Oil Operator | Dec 2022 |
| 670 | Washakie Energies Company | Worland, WY 82401 | Oil & Gas Operator | Dec 2019 |
| 671 | Washington Energy Exploration | | Oil & Gas Operator | Dec 1997 |
| 672 | Wave Petroleum Operating LLC | Denver, CO 80202 | Oil & Gas Operator | May 2025 |
| 673 | Weaver Oil Inc | | Oil & Gas Operator | Oct 2011 |
| 674 | Wellstar Corporation | Northglenn, CO 80233 | Oil & Gas Operator | May 2025 |
| 675 | Wem Joint Venture | Gillette, WY 82716 | Oil & Gas Operator | Sep 2015 |
| 676 | Wesco Operating, Inc. | Casper, WY 82602 | Oil & Gas Operator | May 2025 |
| 677 | Wessely Energy Corporation | | Oil & Gas Operator | Feb 1989 |
| 678 | West Gas Inc | | Oil & Gas Operator | Dec 2017 |
| 679 | Westburne Petroleum Inc | | Oil Operator | Jun 1990 |
| 680 | Westech Energy Corporation | Denver, CO 80237 | Oil & Gas Operator | Mar 2011 |
| 681 | Western American Resources LLC | Denver, CO 80202 | Oil & Gas Operator | Jun 2024 |
| 682 | Western Gas Resources Inc | Denver, CO 80202 | Oil & Gas Operator | Dec 2004 |
| 683 | Western Interior Energy Inc. | Denver, CO 80202 | Oil & Gas Operator | Jul 2020 |
| 684 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 685 | Wexpro Company | Rock Springs, WY 82902-0458 | Oil & Gas Operator | May 2025 |
| 686 | Wheless Drilling Company | | Oil & Gas Operator | Dec 1989 |
| 687 | White Rock Oil & Gas, LLC | Plano, TX 75024 | Oil & Gas Operator | Jul 2025 |
| 688 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Jul 2025 |
| 689 | Wichita River Oil Corporation | Englewood, CO 80111 | Oil & Gas Operator | Apr 2009 |
| 690 | Wildfire Partners Inc | Ardmore, OK 73402 | Oil & Gas Operator | Dec 2009 |
| 691 | Williams Exploration Company | | Oil & Gas Operator | Dec 1986 |
| 692 | Williams Ted H | | Oil & Gas Operator | Dec 2008 |
| 693 | Winco Petroleum Corp | Denver, CO 80202 | Oil & Gas Operator | Dec 1997 |
| 694 | Windsor Energy Group LLC | Oklahoma City, OK 73118 | Oil & Gas Operator | Aug 2021 |
| 695 | Winter Ridge Energy LLC | Denver, CO 80202 | Oil & Gas Operator | Sep 2011 |
| 696 | WLP Oil Inc | Gillette, WY 82717 | Oil & Gas Operator | Dec 2018 |
| 697 | Wold Energy Partners LLC | Denver, CO 80202 | Oil & Gas Operator | Feb 2022 |
| 698 | Wold Oil & Gas | | Oil & Gas Operator | Oct 1996 |
| 699 | Wold Oil Properties Inc | Denver, CO 80203 | Oil & Gas Operator | Feb 2018 |
| 700 | Wolf Energy Company | | Oil & Gas Operator | Dec 1985 |