| 401 | Merrion Oil & Gas Corp | Farmington, NM 87401 | Oil & Gas Operator | Aug 2025 |
| 402 | Methane Productions Inc | Recluse, WY 82725 | Oil & Gas Operator | Apr 2007 |
| 403 | Meyer Douglas P | Longmont, CO 80501 | Oil & Gas Operator | Aug 2006 |
| 404 | Michigan-Wisconsin Pipe Line Co | | Oil & Gas Operator | Dec 1983 |
| 405 | Mid-Con Energy Operating, LLC | Tulsa, OK 74136 | Oil & Gas Operator | Aug 2025 |
| 406 | Midgard Energy Company | The Woodlands, TX 77380 | Oil & Gas Operator | Dec 2014 |
| 407 | Minnelusa Oil LLC | Temecula, CA 92589 | Oil Operator | Feb 2002 |
| 408 | Mitchell Energy Corp | Houston, TX 77002 | Oil & Gas Operator | Aug 2013 |
| 409 | Mitchell M J | | Oil & Gas Operator | Jan 1983 |
| 410 | Mobil Expl & Producing North America Inc | | Oil & Gas Operator | Nov 1986 |
| 411 | Monahan Rex | Sterling, CO 80751 | Oil & Gas Operator | Jun 2002 |
| 412 | Moncrief W A Jr | Fort Worth, TX 76102 | Oil & Gas Operator | Aug 2025 |
| 413 | Monsanto Company | Indianapolis, IN 46280 | Oil & Gas Operator | Jan 2005 |
| 414 | Montex Drilling Company LLC | Fort Worth, TX 76102 | Oil & Gas Operator | Oct 2025 |
| 415 | Montex Exploration | Sugarland, TX 77478 | Oil Operator | Apr 2003 |
| 416 | Mosbacher Production Co. | Houston, TX 77001 | Oil & Gas Operator | Aug 1984 |
| 417 | Mountain Hawk Energy LLC | Athens, TX 75751 | Gas Operator | Jan 2015 |
| 418 | MTG Operating Inc | Ridgeland, MS 39158 | Gas Operator | Apr 2011 |
| 419 | Mull Drilling Company | Wichita, KS 67206 | Oil & Gas Operator | Aug 2025 |
| 420 | Murphy Oil USA Inc | New Orleans, LA 70161 | Oil & Gas Operator | Jan 1993 |
| 421 | Murphy Sheldon L & Loretta | Newcastle, WY 82701 | Oil & Gas Operator | Aug 2025 |
| 422 | MWJ Producing Company | Midland, TX 79701 | Oil & Gas Operator | Jul 1998 |
| 423 | Nadel And Gussman Rockies, LLC | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2012 |
| 424 | Nance Petroleum Corporation | Billings, MT 59103-7168 | Oil & Gas Operator | Nov 2007 |
| 425 | National Energy Group, Inc. | Dallas, TX 75206 | Oil & Gas Operator | Sep 2014 |
| 426 | National Oil Company | Garden City, KS 67846 | Oil & Gas Operator | Jun 2024 |
| 427 | National Pride Operating | Parker, CO 80134 | Oil & Gas Operator | Dec 2017 |
| 428 | Natomas North America Inc | | Oil & Gas Operator | Aug 1993 |
| 429 | Navigation Powder River LLC | Houston, TX 77024 | Oil & Gas Operator | Aug 2025 |
| 430 | Neward Corporation | FT. Worth, TX 76102 | Oil & Gas Operator | Dec 1997 |
| 431 | Newport Gas Partners LLC | Gillette, WY 82716 | Oil & Gas Operator | May 2025 |
| 432 | Nicolaysen G G Jr | | Oil & Gas Operator | Dec 1995 |
| 433 | Nicor Exploration | | Oil Operator | Jul 1993 |
| 434 | Nicor Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Jun 1993 |
| 435 | Nielson & Associates Inc | Cody, WY 82414 | Oil & Gas Operator | Feb 2016 |
| 436 | Noble Energy Inc | Midland, TX 79706 | Oil & Gas Operator | Oct 2025 |
| 437 | Nonsuch Natural Gas Inc | Naples, FL 34108 | Oil & Gas Operator | Jun 2025 |
| 438 | Norcen Energy Inc | | Oil Operator | Dec 1989 |
| 439 | Nordstrand Engineering Inc | Houston, TX 77019 | Oil & Gas Operator | Oct 2025 |
| 440 | North Finn LLC | Casper, WY 82605 | Oil & Gas Operator | Aug 2025 |
| 441 | Northern Production Co | Gillette, WY 82717 | Oil & Gas Operator | Apr 2013 |
| 442 | Northstar Operating Company | Midland, TX 79702 | Oil & Gas Operator | Jun 2024 |
| 443 | Norton Frickey | Lakewood, CO 80215 | Oil & Gas Operator | Dec 2023 |
| 444 | Nova Energy Inc | Casper, WY 82601 | Oil & Gas Operator | Oct 2020 |
| 445 | O'Brien Energy Resources Corp | Portsmouth, NH 03801 | Oil & Gas Operator | Oct 2025 |
| 446 | Ocean Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 447 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Jun 2025 |
| 448 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | Sep 2025 |
| 449 | Oilfield Salvage & Service Company | Littleton, CO 80120 | Oil & Gas Operator | Aug 2025 |
| 450 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 451 | Oklahoma Oil Company | Dallas, TX 75206 | Oil & Gas Operator | Aug 2013 |
| 452 | Olympic Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Jul 2004 |
| 453 | Opes Production Inc | Buffalo, WY 82834 | Gas Operator | Mar 2015 |
| 454 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 455 | Osborn Heirs Company LTD | San Antonio, TX 78217 | Oil & Gas Operator | Jun 2025 |
| 456 | Oxford Exploration Company | Denver, CO 80237 | Oil & Gas Operator | Aug 1995 |
| 457 | Oxy Petroleum Inc | | Oil & Gas Operator | Jan 1986 |
| 458 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |
| 459 | Qep Energy Company | Midland, TX 79701 | Oil & Gas Operator | Jun 2025 |
| 460 | Quest Operating LLC | Sheridan, WY 82801 | Gas Operator | Sep 2008 |
| 461 | Quicksilver Resources Inc | Fort Worth, TX 76102 | Oil & Gas Operator | Mar 2018 |
| 462 | Quinoco Petroleum Inc | | Oil & Gas Operator | Dec 1990 |
| 463 | Quintana Petroleum Corporation | Denver, CO 80265 | Oil & Gas Operator | Mar 1998 |
| 464 | Rainbow Oil Company | | Oil & Gas Operator | Aug 1999 |
| 465 | Rainbow Resources, Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Aug 2007 |
| 466 | Ranch Oil Company | West Linn, OR 97068 | Oil & Gas Operator | Aug 2025 |
| 467 | Ranger Holdings Co | | Oil & Gas Operator | Jul 1993 |
| 468 | RB Operating Company | Shawnee, OK 74802-1488 | Oil & Gas Operator | Apr 2015 |
| 469 | Reading & Bates Petroleum | | Oil & Gas Operator | Apr 1989 |
| 470 | Red Tiger Oil & Gas LLC | Gillette, WY 82718 | Oil & Gas Operator | Jul 2025 |
| 471 | Redbud E & P, Inc. | Giddings, TX 78942 | Oil & Gas Operator | Oct 2025 |
| 472 | Redstone Resources Inc | Newcastle, WY 82701 | Gas Operator | Dec 2010 |
| 473 | Reef Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Feb 2007 |
| 474 | Reliance Resources Inc | Houston, TX 77007 | Gas Operator | Jun 2012 |
| 475 | Renor Exploration | Englewood, CO 80111 | Oil Operator | Feb 2001 |
| 476 | Reserve Oil & Gas Company | | Oil & Gas Operator | Jul 1981 |
| 477 | Resolute Wyoming Inc | Denver, CO 80203 | Oil & Gas Operator | May 2018 |
| 478 | Resource Enterprises Inc | Salt Lake City, UT 84108 | Gas Operator | Dec 1990 |
| 479 | Resources Investment Corp | Denver, CO 80202 | Oil & Gas Operator | Sep 2018 |
| 480 | Reunion Energy Company | Houston, TX 77056 | Oil & Gas Operator | May 1996 |
| 481 | Richardson Operating Company | Denver, CO 80237 | Oil & Gas Operator | Jul 2025 |
| 482 | Ridge Energy Partners LLC | Casper, WY 82601 | Oil Operator | Dec 2018 |
| 483 | Rim Operating, Inc. | Englewood, CO 80112 | Oil & Gas Operator | Oct 2025 |
| 484 | Rme Petroleum Company | Houston, TX 77251 | Oil & Gas Operator | Nov 2016 |
| 485 | Rochelle Oil & Gas | Gillette, WY 82717 | Oil & Gas Operator | Mar 2024 |
| 486 | Rock Creek Resources LLC | Englewood, CO 80112 | Oil & Gas Operator | Dec 2021 |
| 487 | Rock Oil Corporation | Lawrence, KS 66046 | Oil Operator | Oct 2004 |
| 488 | Rockies Resources Holdings LLC | Lakewood, CO 80228 | Oil & Gas Operator | Jul 2025 |
| 489 | Rocky Mountain Gas Inc | Sheridan, WY 82801 | Gas Operator | Nov 2009 |
| 490 | Roemer Oil Company | Denver, CO 80202 | Oil & Gas Operator | Nov 1998 |
| 491 | Roff Operating Company LLC | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 492 | Royal Resources Exploration | | Oil & Gas Operator | Mar 1984 |
| 493 | Ruby Drilling Company Inc | Gillette, WY 82718 | Oil Operator | Oct 2007 |
| 494 | Sabine Corporation | Oklahoma City, OK 73116 | Oil & Gas Operator | Jul 1996 |
| 495 | Sabine Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 496 | Saga Petroleum LLC Of Colorado | Norman, OK 73072 | Oil & Gas Operator | Oct 2025 |
| 497 | Sage Butte PRB Operating, LLC | Denver, CO 80202 | Oil & Gas Operator | Aug 2025 |
| 498 | Samedan Oil Corporation | Houston, TX 77067 | Oil & Gas Operator | Dec 2019 |
| 499 | Samson Oil & Gas USA Inc | Denver, CO 80202 | Oil & Gas Operator | Aug 2025 |
| 500 | Samson Resources Company LLC | Denver, CO 80202 | Oil & Gas Operator | Feb 2021 |