| 1 | M & M Investments | | Oil & Gas Operator | May 1990 |
| 2 | Mack Energy Co. | Duncan, OK 73534 | Oil & Gas Operator | Jul 2025 |
| 3 | Manursing Island Prod. Corp. | | Oil & Gas Operator | Sep 2002 |
| 4 | Mapco Oil & Gas Company | Tulsa, OK 74101-2115 | Oil & Gas Operator | Jan 1985 |
| 5 | Maple Gulf Coast Props. Corp. | | Oil & Gas Operator | Jun 1989 |
| 6 | Marine Cont. & Supply Inc. | | Oil & Gas Operator | Nov 1985 |
| 7 | Marline Petroleum Corporation | | Oil & Gas Operator | Dec 1985 |
| 8 | Marquee Corporation | Houston, TX 77024 | Oil & Gas Operator | Oct 2025 |
| 9 | Marshall Exploration, Inc. | | Oil & Gas Operator | Jun 1992 |
| 10 | Martin Exploration Co. | | Oil & Gas Operator | Apr 1986 |
| 11 | May Oil & Gas, L.L.C. | | Oil & Gas Operator | Dec 2013 |
| 12 | May Petroleum, Inc. | Dallas, TX 75231 | Oil & Gas Operator | Nov 1998 |
| 13 | McCord Exploration Co. | | Oil & Gas Operator | Dec 1990 |
| 14 | McCormick Operating Company | | Oil & Gas Operator | Mar 1984 |
| 15 | McCormick-Bintliff | | Oil & Gas Operator | Feb 1984 |
| 16 | McGowan Working Partners | Jackson, MS 39296 | Oil & Gas Operator | Dec 2000 |
| 17 | McGowan Working Partners, Inc. | Jackson, MS 39296 | Oil & Gas Operator | Oct 2025 |
| 18 | MCZ, Inc. | Houston, TX 77026 | Oil & Gas Operator | Sep 1990 |
| 19 | Medallion Production Company | Tulsa, OK 74103 | Oil & Gas Operator | May 1997 |
| 20 | Merit Energy Company | Dallas, TX 75240 | Oil & Gas Operator | Oct 2025 |
| 21 | Mertz Energy LLC | Houston, TX 77098 | Oil & Gas Operator | Jan 2025 |
| 22 | Meyers-Lasher, Inc. | | Oil & Gas Operator | Mar 1999 |
| 23 | Mideast Gas Systems, Inc. | Midland, TX 79702 | Oil & Gas Operator | Dec 2005 |
| 24 | Midstates Oil Company | Oklahoma City, OK 73112 | Oil & Gas Operator | Nov 2000 |
| 25 | Midstates Petroleum Company LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 26 | Midstates Petroleum Corp. | | Oil & Gas Operator | Dec 2008 |
| 27 | Milagro Exploration, LLC | Houston, TX 77010 | Oil & Gas Operator | Aug 2018 |
| 28 | Moco Operating Company | | Oil & Gas Operator | Mar 2002 |
| 29 | Mole Operating Co., Inc. | | Oil & Gas Operator | Oct 1983 |
| 30 | Monexco, Inc. | | Oil Operator | Dec 2003 |
| 31 | Moore McCormack Energy, Inc. | | Oil & Gas Operator | Jul 1988 |
| 32 | Murphy Exploration & Prod. Co. | Houston, TX 77094 | Oil & Gas Operator | Jun 2011 |
| 33 | Murphy Oil USA Inc | New Orleans, LA 70161 | Oil & Gas Operator | Jan 1993 |
| 34 | Mustang Energy Inc. | Porter, TX 77365 | Oil & Gas Operator | Mar 2008 |