| 1 | M & M Investments | | Oil & Gas Operator | May 1990 |
| 2 | M. P. S. Prod. Co. | Houston, TX 77225 | Oil & Gas Operator | Dec 1996 |
| 3 | Mack Energy Co. | Duncan, OK 73534 | Oil & Gas Operator | Jul 2025 |
| 4 | Magna Operating, LLC | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 5 | Mapco Oil & Gas Company | Tulsa, OK 74101-2115 | Oil & Gas Operator | Jan 1985 |
| 6 | Mapco Production Co | Billings, MT 59102 | Oil & Gas Operator | Apr 1994 |
| 7 | Maralo, Inc. | Midland, TX 79702 | Oil & Gas Operator | Dec 1998 |
| 8 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Aug 2025 |
| 9 | Marion Corporation | | Oil & Gas Operator | Jan 2001 |
| 10 | Mark L Shidler Inc | Houston, TX 77055 | Oil & Gas Operator | Jul 2025 |
| 11 | Marmaton Oil Company | Houston, TX 77002 | Oil & Gas Operator | Jul 1998 |
| 12 | Marquee Corporation | Houston, TX 77024 | Oil & Gas Operator | Oct 2025 |
| 13 | Marquis Resources, LLC | | Oil & Gas Operator | Jul 2021 |
| 14 | Marshall Petroleum, Inc. | Houston, TX 77040 | Oil & Gas Operator | Aug 2003 |
| 15 | Mayne & Mertz, Inc. | Midland, TX 79702 | Oil & Gas Operator | Mar 2013 |
| 16 | McConathy Production Co.,Inc. | | Oil & Gas Operator | Jun 1990 |
| 17 | McCord Exploration Co. | | Oil & Gas Operator | Dec 1990 |
| 18 | McGowan Working Partners | Jackson, MS 39296 | Oil & Gas Operator | Dec 2000 |
| 19 | McGowan Working Partners, Inc. | Jackson, MS 39296 | Oil & Gas Operator | Oct 2025 |
| 20 | McKenzie Management Inc. | | Oil & Gas Operator | Aug 1989 |
| 21 | McMoran Exploration Company | | Oil & Gas Operator | May 1985 |
| 22 | McMoran Production Co. | | Oil & Gas Operator | May 1985 |
| 23 | MCZ, Inc. | Houston, TX 77026 | Oil & Gas Operator | Sep 1990 |
| 24 | Medders Oil Company | Wichita Falls, TX 76308 | Oil & Gas Operator | Oct 2025 |
| 25 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 26 | Merlin J Verret | | Gas Operator | Jun 1986 |
| 27 | Mideast Gas Systems, Inc. | Midland, TX 79702 | Oil & Gas Operator | Dec 2005 |
| 28 | Midstates Petroleum Company LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 29 | Midstates Petroleum Corp. | | Oil & Gas Operator | Dec 2008 |
| 30 | Miller Oil Field Services, Inc | | Oil Operator | Feb 1990 |
| 31 | Minatome Corpora | | Oil & Gas Operator | Sep 1987 |
| 32 | Miss-Lou Operating LLC | | Oil & Gas Operator | Jul 2025 |
| 33 | Miss-Lou Petroleum LLC | | Oil & Gas Operator | Jun 2011 |
| 34 | Mission Resources Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2008 |
| 35 | Mitchell Energy Company L.P. | Spring, TX 77387 | Oil & Gas Operator | Mar 2008 |
| 36 | Mitchell Energy Corp | Houston, TX 77002 | Oil & Gas Operator | Aug 2013 |
| 37 | Mobil Oil E & P Southeast Inc | | Oil & Gas Operator | Sep 2013 |
| 38 | Moore McCormack Energy, Inc. | | Oil & Gas Operator | Jul 1988 |
| 39 | Moran Exploration, Inc. | | Oil & Gas Operator | Jan 1985 |
| 40 | Mosbacher Energy Company | Houston, TX 77002 | Oil & Gas Operator | Oct 2025 |
| 41 | Murchison Oil & Gas Inc | Plano, TX 75024 | Oil & Gas Operator | May 2024 |
| 42 | MW Petroleum Corporation | Houston, TX 77056 | Oil & Gas Operator | Mar 2015 |