| 1 | M & M Investments | | Oil & Gas Operator | May 1990 |
| 2 | M. F. McCain, Inc. | | Oil & Gas Operator | Jul 1987 |
| 3 | Mack Energy Co. | Duncan, OK 73534 | Oil & Gas Operator | Jul 2025 |
| 4 | Magnum Producing, LP | Corpus Chrsti, TX 78401 | Oil & Gas Operator | Oct 2025 |
| 5 | Manna Minerals, Inc. | | Oil & Gas Operator | Apr 1989 |
| 6 | Manti Exploration Operating LLC | Corpus Chrsti, TX 78403 | Oil & Gas Operator | Feb 2015 |
| 7 | Manti Operating Company | Covington, LA 70435 | Oil & Gas Operator | Oct 2025 |
| 8 | Map Drilling Company | | Oil & Gas Operator | Apr 2012 |
| 9 | Mar-Low Corporation | | Oil & Gas Operator | Mar 1992 |
| 10 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Aug 2025 |
| 11 | Mariner Energy, Inc. | Houston, TX 77042 | Oil & Gas Operator | Nov 2010 |
| 12 | Maritech Resources, LLC | | Oil & Gas Operator | May 2011 |
| 13 | Mark L Shidler Inc | Houston, TX 77055 | Oil & Gas Operator | Jul 2025 |
| 14 | Mark Producing, Inc. | Houston, TX 77057 | Oil & Gas Operator | Dec 1987 |
| 15 | Marline Oil Corporation | Houston, TX 77002 | Oil & Gas Operator | Dec 1989 |
| 16 | Marline Petroleum Corporation | | Oil & Gas Operator | Dec 1985 |
| 17 | Marshall Exploration, Inc. | | Oil & Gas Operator | Jun 1992 |
| 18 | Marshall Prod. & Energy Inc. | | Oil & Gas Operator | Jan 1992 |
| 19 | Martin Exploration Co. | | Oil & Gas Operator | Apr 1986 |
| 20 | Masters Resources, L.L.C. | Houston, TX 77079 | Oil & Gas Operator | Dec 2008 |
| 21 | Maxus Exploration Company | Dallas, TX 75201 | Oil & Gas Operator | Jan 1995 |
| 22 | Maynard Oil Co. | Denver, CO 80202 | Oil & Gas Operator | Sep 2004 |
| 23 | McAlester Fuel Co | Houston, TX 77042 | Oil & Gas Operator | Jan 2010 |
| 24 | McCormick-Bintliff-Pettit | | Oil & Gas Operator | Feb 1984 |
| 25 | McCormick-Terra-Bintliff | | Oil & Gas Operator | Dec 1979 |
| 26 | McGowen Resources Co., Inc. | Dallas, TX 75206 | Oil & Gas Operator | Aug 2003 |
| 27 | McMoran Oil & Gas LLC | New Orleans, LA 70160 | Oil & Gas Operator | Oct 2021 |
| 28 | McRae Oil Corporation | | Oil & Gas Operator | Mar 1984 |
| 29 | Medallion Petroleum, Inc. | Tulsa, OK 74103 | Oil & Gas Operator | Jan 2015 |
| 30 | Medallion Production Company | Tulsa, OK 74103 | Oil & Gas Operator | May 1997 |
| 31 | Memorial Exploration Company | Saint Louis, MO 63105 | Oil & Gas Operator | Aug 1996 |
| 32 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 33 | Merit Energy Company | Dallas, TX 75240 | Oil & Gas Operator | Oct 2025 |
| 34 | Mescalero Energy, Inc. | San Antonio, TX 78231 | Oil & Gas Operator | Aug 2003 |
| 35 | Michel T. Halbouty Energy Co. | | Oil & Gas Operator | Nov 1986 |
| 36 | Mid-Continent Energy, Inc. | Tulsa, OK 74103 | Oil & Gas Operator | Apr 2020 |
| 37 | Middle Bay Production Co. Inc. | Houston, TX 77010 | Oil & Gas Operator | Sep 2014 |
| 38 | Milagro Exploration, LLC | Houston, TX 77010 | Oil & Gas Operator | Aug 2018 |
| 39 | Miller Oil Field Services, Inc | | Oil Operator | Feb 1990 |
| 40 | Miller S.W.D., Inc. | | Oil Operator | Oct 2002 |
| 41 | Minatome Corpora | | Oil & Gas Operator | Sep 1987 |
| 42 | Mission Resources Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2008 |
| 43 | Mobil E&P N.A.-Pel-Tex | | Oil & Gas Operator | Dec 1993 |
| 44 | Mobil E&P North America Inc. | | Oil & Gas Operator | Jan 1994 |
| 45 | Mobil Oil E & P Southeast Inc | | Oil & Gas Operator | Sep 2013 |
| 46 | Mobil Oil E&P Se Inc - Pel-Tex | | Oil & Gas Operator | Dec 2005 |
| 47 | Monterey Pipeline Co. | | Oil Operator | Aug 1993 |
| 48 | Mosbacher Energy Company | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 49 | Mullins & Prichard | | Oil & Gas Operator | May 1992 |
| 50 | Murphy Exp & Prod Co.-USA | | Oil & Gas Operator | May 2014 |
| 51 | Murphy Exploration & Prod. Co. | Houston, TX 77094 | Oil & Gas Operator | Jun 2011 |