| 1 | Mapco Inc | Billings, MT 59102 | Oil & Gas Operator | Dec 1983 |
| 2 | Mapco Oil & Gas Company | Tulsa, OK 74101-2115 | Oil & Gas Operator | Jan 1985 |
| 3 | Mapco Production Co | Billings, MT 59102 | Oil & Gas Operator | Apr 1994 |
| 4 | Mar/Reg Oil Company | Reno, NV 89511 | Oil & Gas Operator | Sep 2025 |
| 5 | Maralex Resources Inc | Ignacio, CO 81137 | Oil & Gas Operator | Sep 2025 |
| 6 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Oct 2025 |
| 7 | Marion Energy Inc | Houston, TX 770082292 | Oil & Gas Operator | May 2015 |
| 8 | Master Pet & Devel Co Inc | Grand Junction, CO 81503 | Oil & Gas Operator | Jul 1999 |
| 9 | Matrix Production Company | Sugar Land, TX 77478 | Oil & Gas Operator | Sep 2025 |
| 10 | Maxus Exploration Company | Dallas, TX 75201 | Oil & Gas Operator | Jan 1995 |
| 11 | McAdams, J F | | Oil Operator | May 1971 |
| 12 | McCulliss Resources Co Inc | Littleton, CO 80161-3248 | Oil & Gas Operator | Jun 2009 |
| 13 | McCulloch Geothermal Corporation | | Oil & Gas Operator | Jun 1982 |
| 14 | McCulloch Oil Corp Of Ca | | Oil & Gas Operator | May 1980 |
| 15 | McElvain Energy Inc | Denver, CO 80265 | Oil & Gas Operator | Nov 2019 |
| 16 | McElvain Oil & Gas Properties Inc | Denver, CO 80265-2080 | Oil & Gas Operator | Jul 2011 |
| 17 | McKenzie Petroleum Company | Houston, TX 77063 | Oil & Gas Operator | Aug 1995 |
| 18 | McKenzie Production Company | Houston, TX 77063 | Oil & Gas Operator | May 1995 |
| 19 | McLish & Luff | Denver, CO 80202 | Gas Operator | Nov 1972 |
| 20 | McLish, Holmes P | Denver, CO 80202 | Oil & Gas Operator | Dec 1983 |
| 21 | McOr Oil & Gas Corp | Houston, TX 77002 | Oil & Gas Operator | Oct 2013 |
| 22 | McRae & Henry LTD | Golden, CO 80401 | Oil & Gas Operator | May 2022 |
| 23 | Medallion Exploration | Holladay, UT 84117 | Oil & Gas Operator | Dec 2015 |
| 24 | Medallion Production Company | Tulsa, OK 74103 | Oil & Gas Operator | May 1997 |
| 25 | Megadon Enterprises, Inc | Salt Lake City, UT 84121 | Oil Operator | May 2020 |
| 26 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 27 | Merit Energy Company | Dallas, TX 75240 | Oil & Gas Operator | Dec 2025 |
| 28 | Merrion & Bayless | Farmington, NM 87401 | Oil & Gas Operator | May 1982 |
| 29 | Merrion Oil & Gas Corp | Farmington, NM 87401 | Oil & Gas Operator | Oct 2025 |
| 30 | Mesa Operating LTD Partnership | Amarillo, TX 79189 | Oil & Gas Operator | May 1994 |
| 31 | Mesa Production Company | Amarillo, TX 79189 | Oil & Gas Operator | Dec 1983 |
| 32 | Miami Oil Producers Inc | Reno, NV 89501 | Oil & Gas Operator | Dec 2012 |
| 33 | Middle Fork Energy Uinta, LLC | Denver, CO 80202 | Oil & Gas Operator | Sep 2025 |
| 34 | Milestone Pet/El Paso Expl | | Oil & Gas Operator | Jul 1985 |
| 35 | Miller Energy Inc | Houston, TX 77024 | Oil & Gas Operator | Oct 2016 |
| 36 | Miller, Dyer & Co LLC | Denver, CO 80202 | Oil & Gas Operator | May 2009 |
| 37 | Mitchell Energy Corp | Houston, TX 77002 | Oil & Gas Operator | Aug 2013 |
| 38 | Mobil Explor & Prod | Cortez, CO 81321 | Oil & Gas Operator | May 2001 |
| 39 | Mobil Oil Corporation | Houston, TX 77210 | Oil & Gas Operator | Dec 2007 |
| 40 | Monahan Rex | Sterling, CO 80751 | Oil & Gas Operator | Jun 2002 |
| 41 | Moncrief Oil | Casper, WY 82602 | Oil & Gas Operator | Feb 1986 |
| 42 | Monsanto | Englewood, CO 80111 | Oil & Gas Operator | Apr 1986 |
| 43 | Moose Mountain Divide #1, LLC | Roosevelt, UT 84066-1656 | Oil & Gas Operator | Oct 2025 |
| 44 | Mountain Fuel Supply Co | Salt Lake City, UT 84139 | Oil & Gas Operator | May 1984 |
| 45 | Mountain Oil And Gas Inc | Roosevelt, UT 84066 | Oil & Gas Operator | Oct 2025 |
| 46 | Mountain Petroleum Corp | Denver, CO 80202 | Oil & Gas Operator | Apr 2013 |
| 47 | Mountain Resource Corporation | Salt Lake City, UT 84124 | Oil & Gas Operator | Dec 1988 |
| 48 | Mountain States Petroleum Corp | Midland, TX 79702 | Oil & Gas Operator | Apr 2008 |
| 49 | Murdoch Oil Co Inc | Bluff, UT 84512 | Oil & Gas Operator | Jun 2010 |
| 50 | Mustang Fuel Corporation | Oklahoma City, OK 73114 | Oil & Gas Operator | Sep 2025 |