| 1 | M. D. & G. Partnership | | Oil & Gas Operator | Dec 1996 |
| 2 | M. H. Whittier Energy LLC | | Oil & Gas Operator | Sep 1996 |
| 3 | M.T. Oil Co. | Copan, OK 74022 | Oil Operator | Jun 2025 |
| 4 | Macpherson Oil Company LLC | | Oil & Gas Operator | Jun 2025 |
| 5 | Macpherson Operating Company L.P. | | Oil & Gas Operator | Jun 2025 |
| 6 | Maranatha Petroleum Inc. | | Oil & Gas Operator | Jul 2025 |
| 7 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Jul 2025 |
| 8 | Marathon Oil Company Operator | | Oil & Gas Operator | Dec 1993 |
| 9 | Marlyn Company | | Oil & Gas Operator | Dec 2009 |
| 10 | Matrix Oil Corporation | | Oil & Gas Operator | Jul 2025 |
| 11 | Maxim Resources LTD U.S.A. | | Oil & Gas Operator | Dec 1997 |
| 12 | Maxoil Inc. | | Oil & Gas Operator | Dec 2004 |
| 13 | Maya Oil LLC | | Oil Operator | Jul 2025 |
| 14 | McFarland Energy, Inc. | New Orleans, LA 70160 | Oil & Gas Operator | Dec 2009 |
| 15 | McLennan Family Properties LLP | | Oil & Gas Operator | Dec 2021 |
| 16 | McOr Oil & Gas Corp | Houston, TX 77002 | Oil & Gas Operator | Oct 2013 |
| 17 | Midway-Sunset Investors LLC | | Oil & Gas Operator | Jul 2025 |
| 18 | Mission Oil Company | | Oil & Gas Operator | Jun 2025 |
| 19 | Mission Resources | | Oil & Gas Operator | Dec 1991 |
| 20 | Mitchell Oil | | Oil Operator | Jun 2025 |
| 21 | Mobil Oil Corporation | Houston, TX 77210 | Oil & Gas Operator | Jun 2016 |
| 22 | Mobil Oil Exploration & Production North America Inc. | | Oil & Gas Operator | Dec 1996 |
| 23 | Monterey Resources Inc. | | Oil & Gas Operator | Dec 1997 |
| 24 | Monument Production Inc. | | Oil & Gas Operator | Dec 2011 |
| 25 | Morrison Oil Co. LLC | | Oil & Gas Operator | Jun 2025 |
| 26 | Mountain VIew Resources LLC | | Oil & Gas Operator | Jul 2025 |