| 501 | Skelly Oil Co | | Oil & Gas Operator | Mar 2005 |
| 502 | Skyline Oil Company | Salt Lake City, UT 84111 | Oil & Gas Operator | Jan 1987 |
| 503 | Skyline Operating Company, LLC | Alpine, UT 84004 | Oil & Gas Operator | May 2025 |
| 504 | Slate River Resources LLC | Denver, CO 80293 | Oil & Gas Operator | Apr 2008 |
| 505 | SM Energy Company | Midland, TX 79707 | Oil & Gas Operator | Jul 2025 |
| 506 | Smoot, Richard P | Salt Lake City, UT 84102 | Oil & Gas Operator | Oct 2010 |
| 507 | Snyder Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | Mar 2015 |
| 508 | Snyder Oil Corporation | Houston, TX 77024 | Oil & Gas Operator | Mar 2008 |
| 509 | Sohio Petroleum Co. | Casper, WY 82602 | Oil & Gas Operator | Apr 1986 |
| 510 | Sohio-Stand Oil Prod Co | Houston, TX 77210-9928 | Oil & Gas Operator | Jan 1989 |
| 511 | Sonat Exploration Co. | Houston, TX 77251 | Oil & Gas Operator | Dec 2021 |
| 512 | Southern Natural Gas Co | Houston, TX 77001 | Oil & Gas Operator | Dec 2011 |
| 513 | Southland Royalty Company | Houston, TX 77210 | Oil & Gas Operator | Sep 2011 |
| 514 | St Oil Company | Denver, CO 80264-2101 | Oil & Gas Operator | Dec 2010 |
| 515 | Standard Oil Co Of Calif | | Oil & Gas Operator | Dec 1983 |
| 516 | Star Oil Operating Company LLC | Laramie, WY 82073 | Oil & Gas Operator | Jun 2025 |
| 517 | Sterling Energy Corporation | Denver, CO 80202 | Oil & Gas Operator | Sep 1995 |
| 518 | Stevenson, Albert | | Oil & Gas Operator | Jun 1979 |
| 519 | Stewart Petroleum Corporation | Greenwood VIllage, CO 80111 | Oil & Gas Operator | Dec 2023 |
| 520 | Stone Energy Corporation | Denver, CO 80202-2828 | Oil & Gas Operator | Oct 2014 |
| 521 | Stone Energy LLC | Denver, CO 80202 | Oil & Gas Operator | May 2005 |
| 522 | Stone, D J | Palo Alto, CA 94301 | Oil & Gas Operator | Sep 1985 |
| 523 | Subsurface Resources Inc | Logan, UT 84321 | Oil & Gas Operator | Aug 1990 |
| 524 | Summit Operating LLC | Boulder, CO 80301 | Oil & Gas Operator | Apr 2025 |
| 525 | Sun Explor & Production Co | Oklahoma City, OK 73126 | Gas Operator | Oct 1984 |
| 526 | Sun Oil Company | Arlington, TX 76006 | Oil & Gas Operator | Dec 2021 |
| 527 | Sunfield Energy Company | Houston, TX 77084-5113 | Oil & Gas Operator | Jul 1999 |
| 528 | Sunray DX Oil Co | | Gas Operator | Dec 1983 |
| 529 | Superior Oil Co. | Denver, CO 80217-5444 | Oil & Gas Operator | Feb 2001 |
| 530 | Supreme X Oil Company | | Oil & Gas Operator | Dec 1983 |
| 531 | Supron Energy Corp | | Oil & Gas Operator | Oct 1995 |
| 532 | Swepi LP | Houston, TX 77079 | Oil & Gas Operator | Jul 2020 |
| 533 | Swepi/Western Division | Houston, TX 77210 | Oil & Gas Operator | Aug 1984 |
| 534 | Swevco-Sabw LLC | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 535 | Synergy Operating LLC | Farmington, NM 87499 | Oil & Gas Operator | Jul 2024 |
| 536 | Tall Dune Resources, LLC | Boerne, TX 78006 | Oil & Gas Operator | Jul 2025 |
| 537 | Tamarack Energy Inc | Midland, TX 79701 | Oil & Gas Operator | Dec 2015 |
| 538 | TCC Royalty Corporation | Centennial, CO 80112 | Gas Operator | Sep 2005 |
| 539 | Tejas Gas Corp | | Oil & Gas Operator | Dec 1974 |
| 540 | Tenneco Oil Company | Oklahoma City, OK 73125 | Oil & Gas Operator | Apr 2025 |
| 541 | Terra Resources, Inc. | Casper, WY 82601 | Oil & Gas Operator | Jun 1990 |
| 542 | Teton Energy Co Inc | Denver, CO 80239 | Oil Operator | Dec 1983 |
| 543 | Texaco E & P Inc | Houston, TX 77099 | Oil & Gas Operator | Jul 2025 |
| 544 | Texaco Inc | Kingfisher, OK 73750 | Oil & Gas Operator | Dec 2017 |
| 545 | Texaco Producing Inc. | Rock Springs, WY 82901 | Oil & Gas Operator | Dec 2000 |
| 546 | Texakoma Oil & Gas Corp | Dallas, TX 75240 | Oil & Gas Operator | Sep 2014 |
| 547 | Texas American Oil Corporation | Midland, TX 79701 | Oil & Gas Operator | Jan 2001 |
| 548 | Texas Eastern Skyline Oil | Houston, TX 77252 | Oil & Gas Operator | Jan 1987 |
| 549 | Texas Oil & Gas | Denver, CO 80264 | Oil & Gas Operator | Oct 1981 |
| 550 | Texoma Production Co | | Oil & Gas Operator | Jun 1986 |
| 551 | The Texas Company | FT Worth, TX 76101 | Oil & Gas Operator | Dec 2013 |
| 552 | Thompson, J C | Denver, CO 80237-2843 | Oil & Gas Operator | Jul 2005 |
| 553 | Three States Natural Gas | | Oil & Gas Operator | Mar 1976 |
| 554 | Thriftway Company | Farmington, NM 87401 | Oil & Gas Operator | Dec 1996 |
| 555 | Thurston Energy Operating | Vernal, UT 84078 | Oil & Gas Operator | Dec 2015 |
| 556 | Tidewater Co | | Oil & Gas Operator | Sep 1967 |
| 557 | Tiger Energy Operating, LLC | Los Angeles, CA 90025 | Oil & Gas Operator | Jun 2019 |
| 558 | Toc Oil Inc | Denver, CO 80202 | Oil & Gas Operator | Jun 2025 |
| 559 | Tola Production Company | Dallas, TX 75367 | Oil & Gas Operator | Jul 2025 |
| 560 | Toledo Mining Co | Irving, TX 75061 | Oil Operator | Dec 1989 |
| 561 | Tom Brown Inc | Denver, CO 80202 | Oil & Gas Operator | Dec 2004 |
| 562 | Total Minatome Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 1998 |
| 563 | Total Petroleum Inc | Houston, TX 77210 | Oil & Gas Operator | Feb 1998 |
| 564 | Transfuel Resources Co | Houston, TX 77215 | Oil & Gas Operator | Aug 2013 |
| 565 | Travis Oil Co | Los Angeles, CA 90024 | Oil Operator | Jan 1990 |
| 566 | Trend Oil Co | Petaluma, CA 94954 | Oil & Gas Operator | Feb 2017 |
| 567 | Triangle Development Co | Mahtomedi, MN 55115 | Gas Operator | Feb 1982 |
| 568 | Tricentrol Resources Inc | Englewood, CO 80111 | Oil & Gas Operator | Jun 1984 |
| 569 | Trigg Drilling Company Inc | Oklahoma City, OK 73105 | Oil & Gas Operator | Jan 2013 |
| 570 | True Oil LLC | Casper, WY 82602 | Oil & Gas Operator | Jun 2025 |
| 571 | Twin Arrow Inc | Rangely, CO 81648 | Oil & Gas Operator | Sep 2009 |
| 572 | Txo Production Corp. | Ganado, TX 77962 | Oil & Gas Operator | Aug 2022 |
| 573 | Uinta Oil & Gas | Roosevelt, UT 84066 | Oil & Gas Operator | Nov 1997 |
| 574 | Uinta Wax Operating, LLC | Fort Worth, TX 76107 | Oil & Gas Operator | May 2025 |
| 575 | Uinta-Taylor Fund, LTD | Roosevelt, UT 84066 | Oil & Gas Operator | Nov 2018 |
| 576 | Uintah Investors LLC | Vernal, UT 84078 | Oil & Gas Operator | May 2025 |
| 577 | Ultra Resources Inc | Houston, TX 77060 | Oil & Gas Operator | Sep 2018 |
| 578 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 579 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 580 | Underwood, Rip C | Amarillo, TX 79101 | Gas Operator | Sep 1963 |
| 581 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 582 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 583 | Union Petrochemical | | Oil & Gas Operator | Dec 1982 |
| 584 | Union Texas Petroleum | Houston, TX 77252 | Oil & Gas Operator | Oct 1991 |
| 585 | United Energy Corporation | San Antonio, TX 78209 | Oil & Gas Operator | Jul 2025 |
| 586 | United Producing Co Inc | | Oil & Gas Operator | May 1961 |
| 587 | United Utilities Corporation | Conroe, TX 77301 | Oil & Gas Operator | Oct 1998 |
| 588 | Universal Resources Corp. | Salt Lake Cty, UT 84145 | Oil & Gas Operator | Jan 2000 |
| 589 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Jul 2025 |
| 590 | Urban, C A & Tersell L W | | Gas Operator | Aug 1937 |
| 591 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | May 2025 |
| 592 | Utah Gas Op LTD | Rangely, CO 81648 | Oil & Gas Operator | May 2025 |
| 593 | Utah-Westar DRL Ventures | Dallas, TX 75201 | Oil & Gas Operator | Nov 1987 |
| 594 | Ute Energy Upstream Holdings LLC | Denver, CO 80202 | Oil & Gas Operator | Dec 2012 |
| 595 | Utex Oil Company | Elko, NV 89803 | Oil & Gas Operator | Dec 1988 |
| 596 | Valley Operating Inc | Denver, CO 80218-3633 | Oil & Gas Operator | Jan 2004 |
| 597 | Vantage Energy Uinta LLC | Denver, CO 80237-2746 | Oil & Gas Operator | Aug 2016 |
| 598 | Vaquero Uinta, LLC | Bakersfield, CA 93309 | Oil & Gas Operator | May 2025 |
| 599 | Vortt Exploration Company, Inc. | Fort Worth, TX 76102 | Oil & Gas Operator | Apr 2019 |
| 600 | Vukasovich Drilling | | Oil & Gas Operator | Mar 1988 |