| 1 | M & R Exploration Company | Houston, TX 77074 | Oil & Gas Operator | Aug 2003 |
| 2 | Mack Energy Co. | Duncan, OK 73534 | Oil & Gas Operator | Jul 2025 |
| 3 | Mannon L. Walters, Inc. | | Oil & Gas Operator | Jun 2024 |
| 4 | Manti Operating Company | Covington, LA 70435 | Oil & Gas Operator | Oct 2025 |
| 5 | Manursing Island Prod. Corp. | | Oil & Gas Operator | Sep 2002 |
| 6 | Marion Corporation | | Oil & Gas Operator | Jan 2001 |
| 7 | Mark L Shidler Inc | Houston, TX 77055 | Oil & Gas Operator | Jul 2025 |
| 8 | Marlin Energy Offshore, L.L.C. | | Oil & Gas Operator | Jun 2006 |
| 9 | Martin-Marks Operating Co. LLC | | Oil & Gas Operator | Dec 2010 |
| 10 | Martineau Petroleum, Inc. | Dallas, TX 75206 | Oil & Gas Operator | Jan 2025 |
| 11 | McGowan Working Partners | Jackson, MS 39296 | Oil & Gas Operator | Dec 2000 |
| 12 | McGowan Working Partners, Inc. | Jackson, MS 39296 | Oil & Gas Operator | Oct 2025 |
| 13 | Meason Operating Company | Natchez, MS 39121 | Oil & Gas Operator | Dec 2011 |
| 14 | Mid-Continent Energy, Inc. | Tulsa, OK 74103 | Oil & Gas Operator | Apr 2020 |
| 15 | Minatome Corpora | | Oil & Gas Operator | Sep 1987 |
| 16 | Miss-Lou Operating LLC | | Oil & Gas Operator | Jul 2025 |
| 17 | Mobil E&P North America Inc. | | Oil & Gas Operator | Jan 1994 |
| 18 | Mobil Oil E & P Southeast Inc | | Oil & Gas Operator | Sep 2013 |
| 19 | Monterey Pipeline Co. | | Oil Operator | Aug 1993 |