| 1 | M V Production Co | | Oil & Gas Operator | Jun 1990 |
| 2 | M V Ventures, G. P. | | Oil & Gas Operator | Dec 2000 |
| 3 | Manti Exploration Operating LLC | Corpus Chrsti, TX 78403 | Oil & Gas Operator | Feb 2015 |
| 4 | Map Drilling Company | | Oil & Gas Operator | Apr 2012 |
| 5 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Aug 2025 |
| 6 | Marlin Coastal, L.L.C. | | Oil & Gas Operator | Apr 2008 |
| 7 | Marlin Energy Offshore, L.L.C. | | Oil & Gas Operator | Jun 2006 |
| 8 | Martin Exploration Co. | | Oil & Gas Operator | Apr 1986 |
| 9 | Maxus Exploration Company | Dallas, TX 75201 | Oil & Gas Operator | Jan 1995 |
| 10 | McCord Exploration Co. | | Oil & Gas Operator | Dec 1990 |
| 11 | McCormick Operating Company | | Oil & Gas Operator | Mar 1984 |
| 12 | McCormick Operating PRTNSHP | | Oil & Gas Operator | Sep 1985 |
| 13 | McFarland Energy, Inc. | New Orleans, LA 70160 | Oil & Gas Operator | Dec 2009 |
| 14 | McGowan Working Partners | Jackson, MS 39296 | Oil & Gas Operator | Dec 2000 |
| 15 | McGowan Working Partners, Inc. | Jackson, MS 39296 | Oil & Gas Operator | Oct 2025 |
| 16 | McMoran Oil & Gas LLC | New Orleans, LA 70160 | Oil & Gas Operator | Oct 2021 |
| 17 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 18 | Meridian Oil Offshore Inc. | | Oil & Gas Operator | Aug 1996 |
| 19 | Midstates Petroleum Company LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 20 | Millennium Offshore Group, Inc. | Houston, TX 77007 | Oil & Gas Operator | Sep 2005 |
| 21 | Mobil E&P North America Inc. | | Oil & Gas Operator | Jan 1994 |
| 22 | Moco Operating Company | | Oil & Gas Operator | Mar 2002 |
| 23 | Mongrue Oil Company, Inc. | | Oil & Gas Operator | Oct 1999 |
| 24 | Mongrue, Roland, Inc | | Oil & Gas Operator | Mar 1979 |
| 25 | Mullins & Prichard | | Oil & Gas Operator | May 1992 |