| 401 | Mar/Reg Investments | Irving, TX 75016 | Oil & Gas Operator | Jul 1999 |
| 402 | Mar/Reg Oil Company | Reno, NV 89511 | Oil & Gas Operator | May 2025 |
| 403 | Maralex Resources Inc | Ignacio, CO 81137 | Oil & Gas Operator | May 2025 |
| 404 | Maralo, Inc. | Midland, TX 79702 | Oil & Gas Operator | Dec 1998 |
| 405 | Maralo, LLC | Midland, TX 79702 | Oil & Gas Operator | Mar 2008 |
| 406 | Maram Energy Inc | MT Vernon, OH 43050 | Oil & Gas Operator | Dec 2024 |
| 407 | Maran Oil Company | San Antonio, TX 78216 | Oil & Gas Operator | Dec 2020 |
| 408 | Maran Oil Company, LLC | San Antonio, TX 78216 | Oil & Gas Operator | Mar 2022 |
| 409 | Maranatha Energy Corporation | Athens, WV 24712 | Oil & Gas Operator | Dec 2021 |
| 410 | Maranatha Exploration Inc | Killbuck, OH 44637 | Oil & Gas Operator | Dec 1992 |
| 411 | Maranatha Exploration, LP | Wichita Falls, TX 76307 | Oil Operator | Feb 2012 |
| 412 | Maranatha Oil Company | Gonzales, TX 78629 | Oil & Gas Operator | Jul 2025 |
| 413 | Maranatha Petroleum Inc. | | Oil & Gas Operator | Apr 2025 |
| 414 | Marata Oil & Gas Company | Dallas, TX 75225 | Oil & Gas Operator | Aug 2003 |
| 415 | Marathon Corporation | | Oil Operator | Dec 1994 |
| 416 | Marathon Oil Co.-Rocky Mountain Region | Cody, WY 82414 | Oil Operator | Dec 1999 |
| 417 | Marathon Oil Com | | Oil & Gas Operator | Dec 1996 |
| 418 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | May 2025 |
| 419 | Marathon Oil Company Operator | | Oil & Gas Operator | Dec 1993 |
| 420 | Marathon Oil Company/Fina | | Oil & Gas Operator | Jan 2005 |
| 421 | Marathon Oil Ef LLC | Houston, TX 77252 | Oil & Gas Operator | Jul 2025 |
| 422 | Marathon Oil Permian LLC | Midland, TX 79701 | Oil & Gas Operator | May 2025 |
| 423 | Marben Corporation | | Oil Operator | Jul 1995 |
| 424 | Marbet LLC | Edmond, OK 73013-6691 | Oil & Gas Operator | Apr 2025 |
| 425 | Marbil Oil, Inc. | Olney, TX 76374 | Oil & Gas Operator | Jun 2013 |
| 426 | Marbob Energy Corp | Artesia, NM 882110227 | Oil & Gas Operator | Oct 2010 |
| 427 | Marchman, J. E. | Graham, TX 76450 | Oil & Gas Operator | Jul 2009 |
| 428 | Marco Drilling Inc | Monroeville, PA 15146-0278 | Oil & Gas Operator | Dec 2024 |
| 429 | Marco Land & Petroleum, Inc. | | Oil & Gas Operator | Jun 2000 |
| 430 | Marco Oil Co, Inc | Sparta, KY 41086 | Oil Operator | Dec 2021 |
| 431 | Marco Oil Compan | | Oil & Gas Operator | Aug 1992 |
| 432 | Marco Oil Company LLC | Bartlesville, OK 74005 | Oil & Gas Operator | Apr 2025 |
| 433 | Marco Polo Exploration, Inc. | Rosenberg, TX 77471 | Oil & Gas Operator | Dec 1993 |
| 434 | Marcon Operating Company, Inc. | Bridgeport, TX 76426 | Oil & Gas Operator | Oct 2011 |
| 435 | Marconi Exploration, Inc. | Houston, TX 77056 | Oil & Gas Operator | Aug 1997 |
| 436 | Marcum Drilling Co. | Midland, TX 79701 | Oil & Gas Operator | Aug 2002 |
| 437 | Marcus Exploration Inc | Piedmont, OK 73078-0308 | Oil & Gas Operator | Dec 2000 |
| 438 | Mardale Drilling Company | Oklahoma City, OK 73157 | Oil Operator | Nov 1998 |
| 439 | Marden Petroleum Exp Co | Marietta, OH 45750 | Oil & Gas Operator | Dec 1990 |
| 440 | Marden Producing | | Gas Operator | Aug 1990 |
| 441 | Marden Producing Company | Edmond, OK 73083 | Gas Operator | Mar 2025 |
| 442 | Mare Energy | Danville, OH 43014 | Oil & Gas Operator | Dec 2021 |
| 443 | Mare Energy LLC | Danville, OH 43014 | Oil & Gas Operator | Dec 2024 |
| 444 | Marexco | | Oil & Gas Operator | Nov 1994 |
| 445 | Marexco, Inc. | Castle Rock, CO 80104 | Oil & Gas Operator | Mar 2025 |
| 446 | Margaret Merganser Inc | Tionesta, PA 16353-5853 | Oil & Gas Operator | Dec 2008 |
| 447 | Maria L. Andrade | | Oil Operator | Dec 2006 |
| 448 | Mariah Energy Corp. | Austin, TX 78716 | Oil & Gas Operator | Apr 1999 |
| 449 | Mariah Exploration LLC | Pawhuska, OK 74056 | Oil & Gas Operator | Oct 2008 |
| 450 | Mariah Operating Company, LLC | Denver, CO 80201 | Oil & Gas Operator | Dec 2009 |
| 451 | Marianas Operating Co. | Abilene, TX 79601 | Oil & Gas Operator | Aug 2003 |
| 452 | Marieff Petroleum, Inc. | Sagamore Hills, OH 44067 | Gas Operator | Dec 2024 |
| 453 | Marienfeld Exploration | Houston, TX 77005 | Oil & Gas Operator | Mar 1994 |
| 454 | Marienfeld Exploration, Inc. | Ojai, CA 93024 | Oil & Gas Operator | Jul 2025 |
| 455 | Marietta Royalty Co Inc | Stillwater, OK 74076 | Oil & Gas Operator | Dec 1986 |
| 456 | Marina Pacifica Oil Company | | Oil & Gas Operator | Dec 1981 |
| 457 | Marine Cont. & Supply Inc. | | Oil & Gas Operator | Nov 1985 |
| 458 | Marine Properties, Inc. | | Oil & Gas Operator | Feb 1995 |
| 459 | Mariner Energy, Inc. | Houston, TX 77042 | Oil & Gas Operator | Nov 2010 |
| 460 | Marino, Charles B. | Tomball, TX 77377 | Oil & Gas Operator | Jul 2025 |
| 461 | Marion Corporation | | Oil & Gas Operator | Jan 2001 |
| 462 | Marion County Prod. Co., L.L.C. | Kilgore, TX 75663 | Oil & Gas Operator | Jul 2025 |
| 463 | Marion Energy Inc | Houston, TX 770082292 | Oil & Gas Operator | May 2015 |
| 464 | Marion Operating Corp | Marion, OH 43301 | Oil & Gas Operator | Dec 2020 |
| 465 | Mariposa Petroleum Co. | | Gas Operator | Dec 1980 |
| 466 | Maritech Resources, Inc. | The Woodlands, TX 77380 | Oil & Gas Operator | Nov 2009 |
| 467 | Maritech Resources, LLC | | Oil & Gas Operator | May 2011 |
| 468 | Marjac Energy Co | Bremen, OH 43107 | Oil & Gas Operator | Dec 1986 |
| 469 | Marjac Oil Company, Inc. | Breckenridge, TX 76424 | Oil & Gas Operator | Jul 2025 |
| 470 | Marjo Incorporat | | Oil & Gas Operator | Jun 1990 |
| 471 | Marjo Oil Company | Lockhart, TX 78644 | Oil & Gas Operator | Oct 1999 |
| 472 | Marjo Operating Company Inc | Tulsa, OK 741010729 | Oil & Gas Operator | Apr 2025 |
| 473 | Marjo Operating Mid-Continent LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2025 |
| 474 | Marjo, Inc. | | Oil & Gas Operator | Sep 1991 |
| 475 | Mark & Troy Johnson | Sugar Grove, PA 16350-5938 | Oil Operator | Dec 2024 |
| 476 | Mark A & Michael J Midlik | Warren, PA 16365-2029 | Oil & Gas Operator | Dec 2015 |
| 477 | Mark A Meier Dba MSC Oil And Gas Co | Oklahoma City, OK 73105 | Oil & Gas Operator | May 2025 |
| 478 | Mark F Preddy & Associates,Inc | | Oil & Gas Operator | Dec 1987 |
| 479 | Mark Holloway Inc | Oklahoma City, OK 73107-6526 | Oil & Gas Operator | Apr 2025 |
| 480 | Mark I Oil Company | Midland, TX 79702 | Oil & Gas Operator | Jul 2025 |
| 481 | Mark III Oil, Inc. | Wichita, KS 67206 | Oil Operator | Dec 2009 |
| 482 | Mark IV Energy | San Antonio, TX 78213 | Oil & Gas Operator | Apr 1993 |
| 483 | Mark L Shidler Inc | Houston, TX 77055 | Oil & Gas Operator | May 2025 |
| 484 | Mark Oil, Inc. | Chanute, KS 66720 | Oil Operator | Feb 2025 |
| 485 | Mark Petroleum Inc | Tulsa, OK 74136 | Oil & Gas Operator | Sep 2018 |
| 486 | Mark Producing, Inc. | Houston, TX 77057 | Oil & Gas Operator | Dec 1987 |
| 487 | Mark Resources Corp | Pittsburgh, PA 15276 | Oil & Gas Operator | Dec 1993 |
| 488 | Mark Seifer | | Oil & Gas Operator | Dec 2024 |
| 489 | Mark T. Kellner Oil Co. | Olean, NY 14760 | Oil & Gas Operator | Dec 2024 |
| 490 | Mark V Petroleum Company | | Oil & Gas Operator | Feb 2020 |
| 491 | Markan Oil Incor | | Oil Operator | Mar 1991 |
| 492 | Markay Oil & Gas Company | Midland, TX 79701 | Oil & Gas Operator | Sep 1998 |
| 493 | Marker Oil Compa | | Oil Operator | Jul 1985 |
| 494 | Market Street Energy, Inc. | Flatonia, TX 78941 | Oil & Gas Operator | Jul 2025 |
| 495 | Markham, Charles A., Jr. & Janet E. | Gowanda, NY 14070 | Gas Operator | Dec 2024 |
| 496 | Markley Exploration | Bixby, OK 74008-5332 | Oil & Gas Operator | Jan 2014 |
| 497 | Markley L C Corporation | Fletcher, OK 73541 | Oil & Gas Operator | Aug 2002 |
| 498 | Marks & Co., Inc. | | Oil & Gas Operator | Dec 2021 |
| 499 | Marks And Garner Production LTD Co | Hobbs, NM 88241 | Oil & Gas Operator | Sep 2010 |
| 500 | Marks Operating LLC | | Oil & Gas Operator | Jul 2016 |