| 401 | Morgan Enterprises | | Oil & Gas Operator | Aug 1997 |
| 402 | Moro Bay Oil Company, Inc. | | Oil Operator | Jan 1997 |
| 403 | Mosbacher Energy Company | Houston, TX 77002 | Oil & Gas Operator | Mar 2025 |
| 404 | Moseley Petroleum Corp. | | Oil & Gas Operator | Apr 1988 |
| 405 | Mountain Front Pipeline Co Inc | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 406 | MRD Operating LLC | | Oil & Gas Operator | Dec 2016 |
| 407 | Mrs. C. M. Roberson | | Oil Operator | Mar 1989 |
| 408 | Mrs. Cecile Andries & Sons | | Oil Operator | Dec 2006 |
| 409 | Mrs. Clara B. Guthrie | | Gas Operator | Jun 1996 |
| 410 | MRT Exploration Co | | Oil & Gas Operator | Feb 1983 |
| 411 | MTBB Acquisition Company, LLC | Houston, TX 77002 | Oil & Gas Operator | Aug 2022 |
| 412 | Mullen Exploration Inc | | Oil & Gas Operator | Dec 2002 |
| 413 | Mullins & Prichard | | Oil & Gas Operator | May 1992 |
| 414 | Munday Operating Co., L.L.C. | | Oil & Gas Operator | May 2007 |
| 415 | Munoco Co. | El Dorado, AR 71730 | Oil & Gas Operator | Jul 2021 |
| 416 | Murchison Oil & Gas Inc | Plano, TX 75024 | Oil & Gas Operator | Mar 2024 |
| 417 | Murexco Petroleum, Inc. | Dallas, TX 75251 | Oil & Gas Operator | Oct 1996 |
| 418 | Murphrey Oil Co | | Oil Operator | Jan 2025 |
| 419 | Murphy - Sun | | Oil & Gas Operator | May 1989 |
| 420 | Murphy Exp & Prod Co.-USA | | Oil & Gas Operator | May 2014 |
| 421 | Murphy Exploration & Prod. Co. | Houston, TX 77094 | Oil & Gas Operator | Jun 2011 |
| 422 | Murphy Oil USA Inc | New Orleans, LA 70161 | Oil & Gas Operator | Jan 1993 |
| 423 | Murray J. Evans | | Oil Operator | Mar 1985 |
| 424 | Muslow And Parker | | Oil & Gas Operator | Jul 1994 |
| 425 | Muslow Oil Industries | | Oil Operator | Jan 1995 |
| 426 | Mustang Energy Inc. | Porter, TX 77365 | Oil & Gas Operator | Mar 2008 |
| 427 | Mustang Energy L C | | Oil & Gas Operator | Jan 2013 |
| 428 | MVM Resources Louisiana L.L.C. | | Oil & Gas Operator | Jan 2025 |
| 429 | MVP Production Inc. | | Oil & Gas Operator | Apr 2005 |
| 430 | MW Petroleum Corporation | Houston, TX 77056 | Oil & Gas Operator | Mar 2015 |