| 1 | M & Z Engineering, Inc. | | Oil & Gas Operator | May 1998 |
| 2 | M. F. McCain, Inc. | | Oil & Gas Operator | Jul 1987 |
| 3 | Magnum Producing & Operating Co. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Jan 2004 |
| 4 | Main Energy, Inc. | Houston, TX 77079 | Oil & Gas Operator | May 2009 |
| 5 | Mandalay Oil & Gas, L.L.C. | | Oil & Gas Operator | May 2008 |
| 6 | Mannon L. Walters, Inc. | | Oil & Gas Operator | Jun 2024 |
| 7 | Map Drilling Company | | Oil & Gas Operator | Apr 2012 |
| 8 | Maple Gulf Coast Props. Corp. | | Oil & Gas Operator | Jun 1989 |
| 9 | Marion Corporation | | Oil & Gas Operator | Jan 2001 |
| 10 | Maritech Resources, LLC | | Oil & Gas Operator | May 2011 |
| 11 | Marsh Engineering, Inc. | | Oil & Gas Operator | Dec 1990 |
| 12 | Marshall Exploration, Inc. | | Oil & Gas Operator | Jun 1992 |
| 13 | Marshall Prod. & Energy Inc. | | Oil & Gas Operator | Jan 1992 |
| 14 | Marshland Exploration Company | | Oil & Gas Operator | May 2006 |
| 15 | Martin Exploration Co. | | Oil & Gas Operator | Apr 1986 |
| 16 | Masters Resources, L.L.C. | Houston, TX 77079 | Oil & Gas Operator | Dec 2008 |
| 17 | May Oil & Gas, L.L.C. | | Oil & Gas Operator | Dec 2013 |
| 18 | McCord Exploration Co. | | Oil & Gas Operator | Dec 1990 |
| 19 | McCord-Goodrich Oil Company | | Oil & Gas Operator | Oct 1991 |
| 20 | McCormick Operating Company | | Oil & Gas Operator | Mar 1984 |
| 21 | McMoran Exploration Company | | Oil & Gas Operator | May 1985 |
| 22 | McMoran Oil & Gas LLC | New Orleans, LA 70160 | Oil & Gas Operator | Oct 2021 |
| 23 | McMoran Production Co. | | Oil & Gas Operator | May 1985 |
| 24 | Medallion Production Company | Tulsa, OK 74103 | Oil & Gas Operator | May 1997 |
| 25 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 26 | Merit Energy Company | Dallas, TX 75240 | Oil & Gas Operator | Oct 2025 |
| 27 | Middle Bay Oil Company, Inc. | Houston, TX 77002 | Oil & Gas Operator | Apr 1998 |
| 28 | Middle Bay Production Co. Inc. | Houston, TX 77010 | Oil & Gas Operator | Sep 2014 |
| 29 | Midnight Drilling LLC | | Oil & Gas Operator | Jan 2016 |
| 30 | Mobil E&P North America Inc. | | Oil & Gas Operator | Jan 1994 |
| 31 | Mobil Oil E & P Southeast Inc | | Oil & Gas Operator | Sep 2013 |
| 32 | Moco Operating Company | | Oil & Gas Operator | Mar 2002 |
| 33 | Moran Exploration, Inc. | | Oil & Gas Operator | Jan 1985 |
| 34 | Mosbacher Energy Company | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 35 | Mullen Exploration Inc | | Oil & Gas Operator | Dec 2002 |
| 36 | Mullins & Prichard | | Oil & Gas Operator | May 1992 |
| 37 | Murphy Exp & Prod Co.-USA | | Oil & Gas Operator | May 2014 |
| 38 | Murphy Exploration & Prod. Co. | Houston, TX 77094 | Oil & Gas Operator | Jun 2011 |
| 39 | Mustang Energy L C | | Oil & Gas Operator | Jan 2013 |
| 40 | MW Petroleum Corporation | Houston, TX 77056 | Oil & Gas Operator | Mar 2015 |