| 401 | South Oak Production Company | | Oil & Gas Operator | Jun 2010 |
| 402 | Southern Union Exploration Co. | Austin, TX 78701 | Oil & Gas Operator | Feb 2002 |
| 403 | Southern Union Production Co. | | Oil Operator | Apr 1979 |
| 404 | Southland Royalty Company | Houston, TX 77210 | Oil & Gas Operator | Sep 2011 |
| 405 | Southwestern Production Corporation | Lakewood, CO 80228 | Oil & Gas Operator | Dec 2025 |
| 406 | Sparrow Oil & Gas LLC | | Oil & Gas Operator | Jan 2026 |
| 407 | Specialized Technological Threading, Inc., | | Oil & Gas Operator | Oct 2019 |
| 408 | Spotted Hawk Development, LLC | | Oil & Gas Operator | Jan 2026 |
| 409 | St Oil Company | Denver, CO 80264-2101 | Oil & Gas Operator | Dec 2010 |
| 410 | St. Mary Land & Exploration Co | Denver, CO 80201 | Oil & Gas Operator | Jun 2010 |
| 411 | Staghorn Energy, LLC | Tulsa, OK 74103 | Oil & Gas Operator | Nov 2025 |
| 412 | Statoil Oil & Gas LP | Austin, TX 78730 | Oil & Gas Operator | Oct 2018 |
| 413 | Stearns Oil Company LLC | Willison, ND 58801 | Oil & Gas Operator | Dec 2025 |
| 414 | Stekoll Oil & Gas, LTD. | | Oil Operator | Jun 1963 |
| 415 | Stephens & Johnson Operating Co. | Wichita Falls, TX 76307 | Oil & Gas Operator | Feb 2026 |
| 416 | Stephens Energy Company LLC | | Oil & Gas Operator | Feb 2010 |
| 417 | Stephens Williston, LLC Dba Seg Williston, LLC | | Oil & Gas Operator | Jan 2026 |
| 418 | Stone Energy Corporation | Denver, CO 80202-2828 | Oil & Gas Operator | Oct 2014 |
| 419 | Summit Resources, Inc. | Houston, TX 77077 | Oil & Gas Operator | Sep 2016 |
| 420 | Sun Exploration And Production Co | | Oil & Gas Operator | Jan 1990 |
| 421 | Sundance Energy Inc | Denver, CO 80202 | Oil & Gas Operator | Jul 2014 |
| 422 | Superior Oil Co. | Denver, CO 80217-5444 | Oil & Gas Operator | Feb 2001 |
| 423 | Swanson Oil & Gas LLC | Williston, ND 58802 | Oil & Gas Operator | Dec 2025 |
| 424 | T-Boc Inc. | | Oil & Gas Operator | Apr 2016 |
| 425 | T2 Operating Corporation | Denver, CO 80202 | Oil & Gas Operator | Feb 2026 |
| 426 | Taqa USA, Inc. | Centennial, CO 80111 | Oil & Gas Operator | Jul 2020 |
| 427 | Tenneco Oil Company | Oklahoma City, OK 73125 | Oil & Gas Operator | Nov 2025 |
| 428 | Terra Resources, Inc. | Casper, WY 82601 | Oil & Gas Operator | Jun 1990 |
| 429 | Texaco Inc | Kingfisher, OK 73750 | Oil & Gas Operator | Dec 2017 |
| 430 | Texakota, Inc. | Houston, TX 77098 | Oil & Gas Operator | Mar 2021 |
| 431 | Texas Crude Energy, Inc. | Houston, TX 77256 | Oil & Gas Operator | Oct 2012 |
| 432 | Texas Gas Exploration Corp. | | Oil & Gas Operator | Nov 1986 |
| 433 | Thunderbird Resources LP | | Oil & Gas Operator | Apr 2019 |
| 434 | Tiger Oil Company | Dallas, TX 75221 | Oil & Gas Operator | May 2007 |
| 435 | Timberline Production Company LLC | Casper, WY 82601 | Oil & Gas Operator | Oct 2020 |
| 436 | Titan Energy, LLC | | Oil & Gas Operator | Jan 2026 |
| 437 | Tom Brown Inc | Denver, CO 80202 | Oil & Gas Operator | Dec 2004 |
| 438 | Top Operating Company | | Oil & Gas Operator | Jul 2022 |
| 439 | Tracker Resource Development II, LLC | | Oil & Gas Operator | Feb 2011 |
| 440 | Transtexas Gas Corporation | Houston, TX 77265 | Oil & Gas Operator | Aug 2005 |
| 441 | Traverse Oil Co | | Oil & Gas Operator | Nov 1983 |
| 442 | Trek Resources, Inc. | Dallas, TX 75207 | Oil & Gas Operator | Feb 2026 |
| 443 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 444 | Tri-C Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Feb 2026 |
| 445 | Triangle USA Petroleum Corporation | Denver, CO 80202 | Oil & Gas Operator | Jul 2021 |
| 446 | Trio Operating Company, Inc. | Wichita Falls, TX 76307 | Oil & Gas Operator | Apr 2006 |
| 447 | True Oil Company | Casper, WY 82602 | Oil & Gas Operator | Aug 2003 |
| 448 | True Oil LLC | Casper, WY 82602 | Oil & Gas Operator | Jan 2026 |
| 449 | Turtle Mountain Gas & Oil, Inc. | | Oil & Gas Operator | Oct 2006 |
| 450 | TXP Operating Co. | | Oil & Gas Operator | Jul 1992 |
| 451 | Tyrex Oil Company | Casper, WY 82602 | Oil & Gas Operator | May 1997 |
| 452 | Universal Resources Corp. | Salt Lake Cty, UT 84145 | Oil & Gas Operator | Jan 2000 |
| 453 | Upton Resources U.S.A. Inc. | | Oil & Gas Operator | Oct 2013 |
| 454 | Valkyrie Operating LLC | Denver, CO 80202 | Oil & Gas Operator | Jan 2026 |
| 455 | Vanderbilt Resources Corp. | Midland, TX 79701 | Oil & Gas Operator | Nov 1991 |
| 456 | Vanguard Operating, LLC | Houston, TX 77057 | Oil & Gas Operator | Aug 2019 |
| 457 | Vast Operations, LLC | | Oil Operator | Dec 2025 |
| 458 | Vaughn Petroleum, Inc. | Dallas, TX 75219 | Oil & Gas Operator | May 2004 |
| 459 | Versa Operating LLC | | Oil & Gas Operator | May 2022 |
| 460 | Vickers & VIckers | | Oil Operator | Jul 2018 |
| 461 | W. H. Hunt Trust Estate | | Oil & Gas Operator | Mar 1997 |
| 462 | Wacker Oil Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 1996 |
| 463 | Wapiti Operating, LLC | Houston, TX 77043 | Oil & Gas Operator | Feb 2026 |
| 464 | Ward Williston Drilling Co | | Oil & Gas Operator | Dec 1994 |
| 465 | Ward-Williston Company | | Oil & Gas Operator | Apr 2014 |
| 466 | Wesco Operating Inc | Casper, WY 82602 | Oil & Gas Operator | Jan 2026 |
| 467 | Wessely Energy Company | Dallas, TX 75206 | Oil & Gas Operator | May 2001 |
| 468 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 469 | Wgo Resources, LLC | | Oil & Gas Operator | Dec 2025 |
| 470 | White Butte Oil Operations, LLC | | Oil & Gas Operator | Dec 2025 |
| 471 | White Rock Oil & Gas, LLC | Plano, TX 75024 | Oil & Gas Operator | Feb 2026 |
| 472 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 473 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 474 | William Herbert Hunt | | Oil & Gas Operator | Mar 1986 |
| 475 | Williston Hunter ND, LLC | | Oil & Gas Operator | Mar 2014 |
| 476 | Williston Industrial Supply Corporation | Williston, ND 58801 | Oil & Gas Operator | Mar 2012 |
| 477 | Windridge Operating LLC | | Oil & Gas Operator | Dec 2025 |
| 478 | Windsor Energy Group LLC | Oklahoma City, OK 73118 | Oil & Gas Operator | Aug 2021 |
| 479 | Wiser Oil Co | Denver, CO 80202 | Oil & Gas Operator | Dec 2023 |
| 480 | WPX Energy Williston, LLC | | Oil & Gas Operator | Sep 2025 |
| 481 | Wyoming Resources Corporation | Rapid City, SD 57702 | Oil & Gas Operator | Oct 2018 |
| 482 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | Feb 2026 |
| 483 | Zargon Oil (ND) Inc. | | Oil & Gas Operator | Dec 2025 |
| 484 | Zavanna Energy Operating, LLC | | Oil & Gas Operator | Dec 2025 |
| 485 | Zenergy Inc | Tulsa, OK 74136 | Oil & Gas Operator | Dec 2025 |
| 486 | Zenergy Operating Company, LLC | Tulsa, OK 74136 | Oil & Gas Operator | Dec 2016 |
| 487 | Zephyr Williston LLC | | Oil & Gas Operator | Dec 2025 |
| 488 | Zinke & Trumbo, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2007 |