| 401 | North Finn LLC | Casper, WY 82605 | Oil & Gas Operator | Jul 2026 |
| 402 | Northern Production Co | Gillette, WY 82717 | Oil & Gas Operator | Apr 2013 |
| 403 | Northstar Operating Company | Midland, TX 79702 | Oil & Gas Operator | Jun 2024 |
| 404 | Norton Frickey | Lakewood, CO 80215 | Oil & Gas Operator | Dec 2023 |
| 405 | Nova Energy Inc | Casper, WY 82601 | Oil & Gas Operator | Oct 2020 |
| 406 | O'Brien Energy Resources Corp | Portsmouth, NH 03801 | Oil & Gas Operator | Sep 2026 |
| 407 | Ocean Energy Inc | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 408 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Jun 2026 |
| 409 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | Jul 2026 |
| 410 | Oilfield Salvage & Service Company | Littleton, CO 80120 | Oil & Gas Operator | Jun 2026 |
| 411 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | May 2026 |
| 412 | Oklahoma Oil Company | Dallas, TX 75206 | Oil & Gas Operator | Aug 2013 |
| 413 | Olympic Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Jul 2004 |
| 414 | Opes Production Inc | Buffalo, WY 82834 | Gas Operator | Mar 2015 |
| 415 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 416 | Osborn Heirs Company LTD | San Antonio, TX 78217 | Oil & Gas Operator | Apr 2026 |
| 417 | Oxford Exploration Company | Denver, CO 80237 | Oil & Gas Operator | Aug 1995 |
| 418 | Oxy Petroleum Inc | | Oil & Gas Operator | Jan 1986 |
| 419 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Sep 2026 |
| 420 | P & M Petroleum Management LLC | Denver, CO 80202 | Oil & Gas Operator | Oct 2021 |
| 421 | P & P Producing Inc | Midland, TX 79702 | Oil & Gas Operator | Feb 2015 |
| 422 | P.O.&G. Operating, LLC | Houston, TX 77057 | Oil & Gas Operator | Sep 2026 |
| 423 | Pacific Enterprises Oil Co USA | Dallas, TX 75201 | Oil & Gas Operator | Feb 2001 |
| 424 | Palo Petroleum, Inc. | Dallas, TX 75360 | Oil & Gas Operator | Sep 2026 |
| 425 | Park Robert E | | Oil Operator | May 1983 |
| 426 | Parker & Parsley Producing LP | Midland, TX 79702 | Oil & Gas Operator | Oct 1997 |
| 427 | Pathfinder Energy Inc | Casper, WY 82605 | Oil & Gas Operator | May 2024 |
| 428 | Patrick Petroleum Co. | Jackson, MI 49201 | Oil & Gas Operator | Nov 1993 |
| 429 | Patriot Energy Resources LLC | Golden, CO 80401 | Gas Operator | Aug 2014 |
| 430 | Patriot Production LLC | Southlake, TX 76092 | Oil & Gas Operator | Apr 2023 |
| 431 | Peabody Natural Gas LLC | Gillette, WY 82718 | Oil & Gas Operator | Jul 2026 |
| 432 | Peak Powder River Resources LLC | Durango, CO 81301 | Oil & Gas Operator | Jun 2026 |
| 433 | Pedco Resources Company | Tulsa, OK 74170 | Oil & Gas Operator | Mar 2008 |
| 434 | Pendragon Energy Partners Inc | Midland, TX 79701 | Oil & Gas Operator | Nov 2009 |
| 435 | Pennaco Energy Incorporated | Gillette, WY 82718 | Oil & Gas Operator | Feb 2021 |
| 436 | Pennzoil Company | Midland, TX 79710-0090 | Oil & Gas Operator | Mar 2000 |
| 437 | Petro Search Exploration Corp | | Oil & Gas Operator | May 1993 |
| 438 | Petro-Canada Resources (USA) Inc | Denver, CO 80202-472 | Oil & Gas Operator | Feb 2010 |
| 439 | Petro-Hunt Corporation | Dallas, TX 75201 | Oil & Gas Operator | Jun 2003 |
| 440 | Petro-Hunt, L.L.C. | Dallas, TX 75201 | Oil & Gas Operator | Sep 2026 |
| 441 | Petro-Lewis Corp. | | Oil & Gas Operator | Feb 1994 |
| 442 | Petrocorp Incorporated | Tulsa, OK 74170 | Oil & Gas Operator | Nov 2021 |
| 443 | Petrogulf Corporation | Denver, CO 80202 | Oil & Gas Operator | Sep 2026 |
| 444 | Petroleum Inc | Wichita, KS 67202 | Oil & Gas Operator | Oct 2021 |
| 445 | Petrox Resources Inc | Meeker, CO 81641 | Oil & Gas Operator | Jul 2026 |
| 446 | Phillips Petroleum Company | Houston, TX 77251 | Oil & Gas Operator | Mar 2013 |
| 447 | Phoenix Resources Co | | Oil & Gas Operator | Jun 1984 |
| 448 | Pine Haven Resources LLC | Boulder, CO 80305 | Oil Operator | Jul 2026 |
| 449 | Pioneer Exploration, LLC | Houston, TX 77090 | Oil & Gas Operator | Jul 2026 |
| 450 | Pioneer Natural Resources USA Inc | Irving, TX 75039 | Oil & Gas Operator | Apr 2026 |
| 451 | Plains Petroleum Operating Co | Denver, CO 80202 | Oil & Gas Operator | Dec 2014 |
| 452 | PML Operating LLC | | Oil Operator | Jul 2026 |
| 453 | Poc-I LLC | Casper, WY 82605 | Oil & Gas Operator | Jul 2026 |
| 454 | Polfam Exploration Co | Denver, CO 80204 | Oil & Gas Operator | Mar 2007 |
| 455 | Polumbus Corporation | Denver, CO 80202 | Oil & Gas Operator | Sep 1982 |
| 456 | Powder River Oil | Golden, CO 80401 | Oil & Gas Operator | Sep 2018 |
| 457 | Powder River Royalty Inc | | Oil & Gas Operator | Dec 1986 |
| 458 | Powerline Energy Corporation | Arlington, TX 76015 | Oil & Gas Operator | Sep 2026 |
| 459 | PRB Oil & Gas Inc | Denver, CO 80202 | Gas Operator | Jul 2008 |
| 460 | Preferred Pipeline Corp. | Victoria, TX 77902 | Oil & Gas Operator | Jul 2026 |
| 461 | Prenalta Corporation | Terrytown, NY 10591 | Oil & Gas Operator | Jan 1997 |
| 462 | Pride Energy Company An Oklahoma GP | Tulsa, OK 74170 | Oil & Gas Operator | Jul 2026 |
| 463 | Prima Exploration, Inc. | Denver, CO 80206 | Oil & Gas Operator | Jul 2026 |
| 464 | Propel Energy Company | | Oil Operator | Oct 1991 |
| 465 | Prospective Invest & Trad Co LTD | Tulsa, OK 74170 | Oil & Gas Operator | Aug 2005 |
| 466 | Provident Resources LTD | | Oil & Gas Operator | Dec 1986 |
| 467 | Puma Petroleum I | | Oil & Gas Operator | Dec 1988 |
| 468 | Pure Petroleum LLC | Gillette, WY 82717 | Oil & Gas Operator | Aug 2011 |
| 469 | Rainbow Oil Company | | Oil & Gas Operator | Aug 1999 |
| 470 | Rainbow Resources, Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Aug 2007 |
| 471 | Ranch Oil Company | West Linn, OR 97068 | Oil & Gas Operator | Jul 2026 |
| 472 | Ranger Holdings Co | | Oil & Gas Operator | Jul 1993 |
| 473 | RB Operating Company | Shawnee, OK 74802-1488 | Oil & Gas Operator | Apr 2015 |
| 474 | Reading & Bates Petroleum | | Oil & Gas Operator | Apr 1989 |
| 475 | Red Rock Resources Corporation | Greenwood VIllage, CO 80111 | Oil & Gas Operator | Jul 2026 |
| 476 | Red Tiger Oil & Gas LLC | Gillette, WY 82718 | Oil & Gas Operator | Jun 2026 |
| 477 | Redbud E & P, Inc. | Giddings, TX 78942 | Oil & Gas Operator | Sep 2026 |
| 478 | Redstone Resources Inc | Newcastle, WY 82701 | Gas Operator | Dec 2010 |
| 479 | Reef Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Feb 2007 |
| 480 | Reliance Resources Inc | Houston, TX 77007 | Gas Operator | Jun 2012 |
| 481 | Renor Exploration | Englewood, CO 80111 | Oil Operator | Feb 2001 |
| 482 | Reserve Oil & Gas Company | | Oil & Gas Operator | Jul 1981 |
| 483 | Resolute Wyoming Inc | Denver, CO 80203 | Oil & Gas Operator | May 2018 |
| 484 | Resource Enterprises Inc | Salt Lake City, UT 84108 | Gas Operator | Dec 1990 |
| 485 | Resources Investment Corp | Denver, CO 80202 | Oil & Gas Operator | Sep 2018 |
| 486 | Reunion Energy Company | Houston, TX 77056 | Oil & Gas Operator | May 1996 |
| 487 | Richardson Operating Company | Denver, CO 80237 | Oil & Gas Operator | Jul 2026 |
| 488 | Ridge Energy Partners LLC | Casper, WY 82601 | Oil Operator | Dec 2018 |
| 489 | Rim Operating, Inc. | Englewood, CO 80112 | Oil & Gas Operator | Sep 2026 |
| 490 | Rme Petroleum Company | Houston, TX 77251 | Oil & Gas Operator | Nov 2016 |
| 491 | Rochelle Oil & Gas | Gillette, WY 82717 | Oil & Gas Operator | Mar 2024 |
| 492 | Rock Creek Resources LLC | Englewood, CO 80112 | Oil & Gas Operator | Dec 2021 |
| 493 | Rock Oil Corporation | Lawrence, KS 66046 | Oil Operator | Oct 2004 |
| 494 | Rockies Resources Holdings LLC | Lakewood, CO 80228 | Oil & Gas Operator | Jul 2026 |
| 495 | Rocky Mountain Gas Inc | Sheridan, WY 82801 | Gas Operator | Nov 2009 |
| 496 | Roemer Oil Company | Denver, CO 80202 | Oil & Gas Operator | Nov 1998 |
| 497 | Roff Operating Company LLC | Houston, TX 77002 | Oil & Gas Operator | Sep 2026 |
| 498 | Royal Resources Exploration | | Oil & Gas Operator | Mar 1984 |
| 499 | Ruby Drilling Company Inc | Gillette, WY 82718 | Oil Operator | Oct 2007 |
| 500 | Sabine Corporation | Oklahoma City, OK 73116 | Oil & Gas Operator | Jul 1996 |