| 1 | Maguire Oil Company | Dallas, TX 75270 | Oil & Gas Operator | Mar 2015 |
| 2 | Mallard Exploration, Inc. | | Oil & Gas Operator | Sep 1975 |
| 3 | Marco Land & Petroleum, Inc. | | Oil & Gas Operator | Jun 2000 |
| 4 | Marion Corporation | | Oil & Gas Operator | Jan 2001 |
| 5 | Mayne & Mertz, Inc. | Midland, TX 79702 | Oil & Gas Operator | Mar 2013 |
| 6 | McCauley Operating Co., Inc. | | Gas Operator | Mar 1999 |
| 7 | McPhearson, Richard E. | | Oil Operator | Mar 1956 |
| 8 | Medallion Exploration | Holladay, UT 84117 | Oil & Gas Operator | Dec 2015 |
| 9 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 10 | Merit Energy Co. Dba Alabama Merit Energy Co., Inc. | | Oil & Gas Operator | Aug 2005 |
| 11 | Michigan Oil Company | FT Worth, TX 76117 | Oil & Gas Operator | Feb 1998 |
| 12 | Midco Energy, Inc. | | Oil & Gas Operator | Dec 1992 |
| 13 | Midroc Operating Co. & Watkins, H. Vaughan, Jr. | | Oil & Gas Operator | Feb 2010 |
| 14 | Midroc Operating Co. & Watkins, H. Vaughan, Jr. & Placid Oil Co. | | Oil & Gas Operator | May 1991 |
| 15 | Midroc Operating Company | | Oil & Gas Operator | Apr 2013 |
| 16 | Miller, W.C. | | Oil & Gas Operator | Jan 1992 |
| 17 | Mississippi Resources, LLC Dba MSR Operating, LLC | | Oil & Gas Operator | May 2021 |
| 18 | Mobay Storage Hub LLC | | Gas Operator | Oct 2008 |
| 19 | Mobil Oil Exploration & Producing Southeast, Inc. | | Oil & Gas Operator | Oct 2025 |
| 20 | Mobile Gulf, Inc. | | Oil & Gas Operator | Aug 1985 |
| 21 | Moon-Hines-Tigrett Operating Co., Inc. | | Oil & Gas Operator | Sep 2025 |
| 22 | Morrow Oil & Gas Co. | Terry, MS 39170 | Oil & Gas Operator | Oct 2025 |
| 23 | Morrow Operating Co., Inc. | | Oil Operator | Mar 2003 |
| 24 | Mosbacher Production Co. | Casper, WY 82602 | Oil & Gas Operator | Aug 1984 |
| 25 | Mosbacher, Robert-Pruet, Chesley | | Oil & Gas Operator | Dec 1983 |
| 26 | Munoco Co. L.C. | | Oil & Gas Operator | Jun 2003 |
| 27 | Munoco Company | El Dorado, AR 71730 | Oil & Gas Operator | Jul 2021 |
| 28 | Murphy Production Co. (Inc.) | | Oil & Gas Operator | Apr 1991 |
| 29 | MWJ Producing Company | Midland, TX 79701 | Oil & Gas Operator | Jul 1998 |