| 1901 | Monarch Energy LLC | Paola, KS 66071 | Oil Operator | Jun 2025 |
| 1902 | Monarch Operating Company | Graham, TX 76450 | Oil & Gas Operator | Jun 2006 |
| 1903 | Monarch Petroleum Corporation | FT Worth, TX 76102 | Oil & Gas Operator | Dec 2019 |
| 1904 | Moncrief Oil | Casper, WY 82602 | Oil & Gas Operator | Feb 1986 |
| 1905 | Moncrief R W Inc | Fort Worth, TX 76102 | Oil & Gas Operator | Dec 1994 |
| 1906 | Moncrief W A Jr | Fort Worth, TX 76102 | Oil & Gas Operator | Aug 2025 |
| 1907 | Moncrief, C. B. | Fort Worth, TX 76102 | Oil & Gas Operator | Aug 2021 |
| 1908 | Monday Creek Resources LTD | Logan, OH 43138 | Oil Operator | Dec 2024 |
| 1909 | Mondiale Energy, Inc. | Brownwood, TX 76801 | Oil & Gas Operator | Oct 2025 |
| 1910 | Mondo Operating Company | Kilgore, TX 75663 | Oil & Gas Operator | Oct 2025 |
| 1911 | Monex | | Oil Operator | Apr 1988 |
| 1912 | Monexco | Edmond, OK 73034-3776 | Oil & Gas Operator | Mar 2008 |
| 1913 | Monexco LLC | Dallas, TX 75204-2634 | Oil & Gas Operator | Jun 2025 |
| 1914 | Monexco Operating Company | Dallas, TX 75204-2634 | Oil & Gas Operator | Jun 2025 |
| 1915 | Monexco, Inc. | | Oil Operator | Dec 2003 |
| 1916 | Monfort, Roy C. | Iola, KS 66749 | Oil & Gas Operator | Sep 1989 |
| 1917 | Monge Oil Corp. | | Oil & Gas Operator | Dec 2021 |
| 1918 | Mongoose Energy, LLC | San Antonio, TX 78209 | Oil & Gas Operator | Oct 2025 |
| 1919 | Mongrue Oil Company, Inc. | | Oil & Gas Operator | Oct 1999 |
| 1920 | Mongrue, Roland, Inc | | Oil & Gas Operator | Mar 1979 |
| 1921 | Monitor O&G, L.L.C. | Frisco, TX 75034 | Oil & Gas Operator | Jan 2016 |
| 1922 | Monona LLC | Ligonier, PA 15658-0612 | Gas Operator | Jul 2025 |
| 1923 | Monroe Gas Associates-1 | | Gas Operator | Mar 2000 |
| 1924 | Monroe Gas Joint Venture | | Gas Operator | Sep 2011 |
| 1925 | Monroe James | | Oil & Gas Operator | Oct 1997 |
| 1926 | Monroe Natural Gas Inc | Norman, OK 73071 | Oil & Gas Operator | Jun 2025 |
| 1927 | Monroe Res LTD | Fairport, NY 14450-3218 | Gas Operator | Dec 2004 |
| 1928 | Monroe Well Ser-Amsterdam | | Oil Operator | Dec 1988 |
| 1929 | Monroe Well Ser-La Petr Assoc | | Oil Operator | Dec 1988 |
| 1930 | Monroe Well Ser-La Petro II | | Oil Operator | Dec 1988 |
| 1931 | Monroe Well Ser-New American85 | | Oil Operator | Dec 1988 |
| 1932 | Monroe Well Ser-Ocean Petr '84 | | Oil & Gas Operator | Dec 1988 |
| 1933 | Monroe Well Ser-Ocean Yacht II | | Oil Operator | May 1989 |
| 1934 | Monroe Well Ser-Oceanyacht1985 | | Oil Operator | Dec 1988 |
| 1935 | Monroe Well Ser-Riverside 1985 | | Oil Operator | Dec 1988 |
| 1936 | Monroe Well Serv-New American | | Oil Operator | Dec 1988 |
| 1937 | Monroe Well Serv-Northern La | | Oil Operator | Dec 1988 |
| 1938 | Monroe Well Serv-Omega 1985 | | Oil Operator | Dec 1988 |
| 1939 | Monroe Well Service | | Oil & Gas Operator | Apr 1998 |
| 1940 | Monroe Well Service-Ajk | | Oil Operator | Dec 1988 |
| 1941 | Monroe Well Service-Apk | | Oil Operator | Dec 1988 |
| 1942 | Monroe Well Service-Beaver1985 | | Oil Operator | Nov 1991 |
| 1943 | Monroe Well Service-Broadway | | Oil Operator | Dec 1988 |
| 1944 | Monroe Well Service-BWK | | Oil Operator | Dec 1988 |
| 1945 | Monroe Well Service-Columbus | | Oil Operator | Dec 1988 |
| 1946 | Monroe Well Service-Das | | Oil Operator | Mar 1989 |
| 1947 | Monroe Well Service-Derrick | | Oil Operator | Dec 1988 |
| 1948 | Monroe Well Service-East End | | Oil Operator | Dec 1988 |
| 1949 | Monroe Well Service-Empire | | Oil Operator | Dec 1988 |
| 1950 | Monroe Well Service-Energy | | Oil Operator | Dec 1988 |
| 1951 | Monroe Well Service-Energy 84 | | Oil Operator | Aug 1989 |
| 1952 | Monroe Well Service-Ged | | Oil Operator | Dec 1988 |
| 1953 | Monroe Well Service-Gotham | | Oil Operator | Apr 1992 |
| 1954 | Monroe Well Service-Gramercy | | Oil Operator | May 1992 |
| 1955 | Monroe Well Service-HGC | | Oil Operator | Dec 1988 |
| 1956 | Monroe Well Service-Lebo | | Oil Operator | Jun 1989 |
| 1957 | Monroe Well Service-Lexington | | Oil Operator | Feb 1989 |
| 1958 | Monroe Well Service-Newtown | | Oil Operator | Aug 1990 |
| 1959 | Monroe Well Service-Ocean | | Oil Operator | Feb 1989 |
| 1960 | Monroe Well Service-Oceanyacht | | Oil Operator | Jan 1989 |
| 1961 | Monroe Well Service-Oil City | | Oil Operator | Aug 1992 |
| 1962 | Monroe Well Service-Omega | | Oil Operator | Aug 1992 |
| 1963 | Monroe Well Service-Par | | Oil Operator | Jan 1990 |
| 1964 | Monroe Well Service-Petrol | | Oil Operator | Sep 1992 |
| 1965 | Monroe Well Service-Petrovest | | Oil Operator | Dec 1988 |
| 1966 | Monroe Well Service-PRG | | Oil Operator | Nov 1990 |
| 1967 | Monroe Well Service-Redstone | | Oil Operator | Jul 1989 |
| 1968 | Monroe Well Service-RVS | | Oil Operator | Dec 1990 |
| 1969 | Monroe Well Service-Shemen | | Oil Operator | Dec 1988 |
| 1970 | Monroe Well Service-Shemen1984 | | Oil Operator | Jan 1989 |
| 1971 | Monroe Well Service-Shemen1985 | | Oil Operator | Nov 1990 |
| 1972 | Monroe Well Service-Sla | | Oil Operator | Mar 1989 |
| 1973 | Monroe Well Service-SPD | | Oil Operator | Dec 1988 |
| 1974 | Monroe Well Service-SPD 1985 | | Oil Operator | Dec 1988 |
| 1975 | Monroe Well Service-TBR | | Oil Operator | Aug 1991 |
| 1976 | Monroe Well Service-TG I | | Oil Operator | Oct 1990 |
| 1977 | Monroe Well Service-TG II | | Oil Operator | Oct 1990 |
| 1978 | Monroe Well Service-TG III | | Oil Operator | Jul 1992 |
| 1979 | Monroe Well Service-TG VI | | Oil Operator | Aug 1989 |
| 1980 | Monroe Well Service-Tpa 1985 | | Oil Operator | Dec 1990 |
| 1981 | Monroe Well Service-Vista | | Oil Operator | Nov 1990 |
| 1982 | Monroe Well Service-West End | | Oil Operator | Dec 1988 |
| 1983 | Monroe Well Service-York | | Oil Operator | Dec 1988 |
| 1984 | Monroe, Cameron | Westfield, NY 14787 | Gas Operator | Dec 2024 |
| 1985 | Monsanto | Englewood, CO 80111 | Oil & Gas Operator | Apr 1986 |
| 1986 | Monsanto Company | Indianapolis, IN 46280 | Oil & Gas Operator | Jan 2005 |
| 1987 | Monsanto Oil Com | | Oil Operator | Nov 1996 |
| 1988 | Monsanto Oil Company | | Oil & Gas Operator | Apr 1986 |
| 1989 | Montalban Oil & Gas Operations, Inc. | Cut Bank, MT 59427 | Oil & Gas Operator | Jul 2025 |
| 1990 | Montana Energy Company, LLC | McAllen, TX 78501 | Oil & Gas Operator | May 2025 |
| 1991 | Montana Heartland LLC | Bismarck, ND 58504 | Oil & Gas Operator | Jun 2025 |
| 1992 | Montana Land & Exploration, Inc. | Calgary, AB T2P 3E7 | Oil & Gas Operator | Apr 2019 |
| 1993 | Montana Land & Mineral Co. | Billings, MT 59105 | Gas Operator | Jun 2025 |
| 1994 | Montana Oil Field Acquisition I, LLC | Rutherford, NJ 07070 | Oil Operator | Jun 2016 |
| 1995 | Montana Power Company | Butte, MT 59701 | Oil & Gas Operator | Apr 2002 |
| 1996 | Montana Power Gas Company | | Oil & Gas Operator | Apr 2002 |
| 1997 | Montani Energy, LLC | Smithville, WV 26178 | Gas Operator | Dec 2021 |
| 1998 | Montare Operating, LTD. | Flower Mound, TX 75022 | Oil & Gas Operator | Oct 2025 |
| 1999 | Montclair Energy LLC | Edmond, OK 73034-7291 | Oil & Gas Operator | Jun 2025 |
| 2000 | Montclair Production Company | Austin, TX 78755 | Oil & Gas Operator | Oct 2025 |