| 401 | Monterey Pipeline Co. | | Oil Operator | Aug 1993 |
| 402 | Monterey Resources LLC | Dallas, TX 75230 | Oil & Gas Operator | Oct 2019 |
| 403 | Moon Operating, Inc. | Longview, TX 75601 | Oil & Gas Operator | Mar 2003 |
| 404 | Moon-Hines-Tigrett Opr Co Inc | | Oil & Gas Operator | Oct 1995 |
| 405 | Moore McCormack Energy, Inc. | | Oil & Gas Operator | Jul 1988 |
| 406 | Moore Oil & Gas-Marion Corp. | | Oil & Gas Operator | Nov 1986 |
| 407 | Moore&Munger Hydrocarbons Inc | | Oil Operator | May 1987 |
| 408 | Mooringsport Energy Prod Corp | | Oil & Gas Operator | Oct 1994 |
| 409 | Mooringsport Energy Trans Corp | | Oil Operator | Apr 1990 |
| 410 | Mor-Co Investments, Inc. | | Gas Operator | Feb 1994 |
| 411 | Moran Exploration, Inc. | | Oil & Gas Operator | Jan 1985 |
| 412 | Moran Oil Co., Inc. | | Oil & Gas Operator | Aug 2009 |
| 413 | Moransco Energy Corporation | Kilgore, TX 75663 | Oil & Gas Operator | Feb 2026 |
| 414 | Morgan Enterprises | | Oil & Gas Operator | Aug 1997 |
| 415 | Moro Bay Oil Company, Inc. | | Oil Operator | Jan 1997 |
| 416 | Mosbacher Energy Company | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 417 | Moseley Petroleum Corp. | | Oil & Gas Operator | Apr 1988 |
| 418 | MRD Operating LLC | | Oil & Gas Operator | Dec 2016 |
| 419 | Mrs. C. M. Roberson | | Oil Operator | Mar 1989 |
| 420 | Mrs. Cecile Andries & Sons | | Oil Operator | Dec 2006 |
| 421 | Mrs. Clara B. Guthrie | | Gas Operator | Jun 1996 |
| 422 | MRT Exploration Co | | Oil & Gas Operator | Feb 1983 |
| 423 | MTBB Acquisition Company, LLC | Houston, TX 77002 | Oil & Gas Operator | Aug 2022 |
| 424 | Mullen Exploration Inc | | Oil & Gas Operator | Dec 2002 |
| 425 | Mullins & Prichard | | Oil & Gas Operator | May 1992 |
| 426 | Munday Operating Co., L.L.C. | | Oil & Gas Operator | May 2007 |
| 427 | Munoco Company | El Dorado, AR 71730 | Oil & Gas Operator | Jul 2021 |
| 428 | Murchison Oil & Gas Inc | Plano, TX 75024 | Oil & Gas Operator | Aug 2020 |
| 429 | Murexco Petroleum Inc | Dallas, TX 75251 | Oil & Gas Operator | Oct 1996 |
| 430 | Murphrey Oil Company, Inc. | | Oil Operator | Jan 2025 |
| 431 | Murphy - Sun | | Oil & Gas Operator | May 1989 |
| 432 | Murphy Exp & Prod Co.-USA | | Oil & Gas Operator | May 2014 |
| 433 | Murphy Exploration & Prod. Co. | Houston, TX 77094 | Oil & Gas Operator | Jun 2011 |
| 434 | Murphy Oil USA, Inc. | New Orleans, LA 70161 | Oil & Gas Operator | Jan 1993 |
| 435 | Murray J. Evans | | Oil Operator | Mar 1985 |
| 436 | Muslow And Parker | | Oil & Gas Operator | Jul 1994 |
| 437 | Muslow Oil Industries | | Oil Operator | Jan 1995 |
| 438 | Mustang Energy Inc. | Porter, TX 77365 | Oil & Gas Operator | Mar 2008 |
| 439 | Mustang Energy L C | | Oil & Gas Operator | Jan 2013 |
| 440 | MVM Resources Louisiana L.L.C. | | Oil & Gas Operator | Jan 2025 |
| 441 | MVP Production Inc. | | Oil & Gas Operator | Apr 2005 |
| 442 | MW Petroleum Corporation | Houston, TX 77056 | Oil & Gas Operator | Mar 2015 |