| 301 | Mississippi Ventures | | Gas Operator | Feb 1992 |
| 302 | Mitchell Energy & Goodrich Oil | | Oil & Gas Operator | Feb 1985 |
| 303 | Mitchell Energy Company L.P. | Spring, TX 77387 | Oil & Gas Operator | Mar 2008 |
| 304 | Mitchell Energy Corp | Houston, TX 77002 | Oil & Gas Operator | Aug 2013 |
| 305 | MJ Energy, LLC | Denver, CO 80206 | Oil Operator | Jan 2025 |
| 306 | MJ Energy, LLC Of Arkansas | | Oil Operator | Jan 2025 |
| 307 | MJB Production Company, Inc. | Brownfield, TX 79316 | Oil & Gas Operator | Mar 2025 |
| 308 | ML Resources, Inc. | Dallas, TX 75240 | Oil & Gas Operator | Mar 2008 |
| 309 | MLGW | | Gas Operator | Sep 1984 |
| 310 | Mobil E&P N.A.-Pel-Tex | | Oil & Gas Operator | Dec 1993 |
| 311 | Mobil E&P N.A.-WM Scully Et Al | | Oil & Gas Operator | Dec 1993 |
| 312 | Mobil E&P North America Inc. | | Oil & Gas Operator | Jan 1994 |
| 313 | Mobil Oil E & P Southeast Inc | | Oil & Gas Operator | Sep 2013 |
| 314 | Mobil Oil E&P Se Inc - Pel-Tex | | Oil & Gas Operator | Dec 2005 |
| 315 | Mobley & Davis | | Oil & Gas Operator | Oct 1986 |
| 316 | Mobley & McCain | | Oil & Gas Operator | Nov 1979 |
| 317 | Mobley & McCain, Et Al | | Oil & Gas Operator | Jul 1986 |
| 318 | Mobley Oil Company, Inc. | | Oil & Gas Operator | Feb 1990 |
| 319 | Mobley Valve Service, Inc. | | Oil & Gas Operator | Nov 2006 |
| 320 | Moco Operating Company | | Oil & Gas Operator | Mar 2002 |
| 321 | Mole Operating Co., Inc. | | Oil & Gas Operator | Oct 1983 |
| 322 | Monarch Petroleum Corporation | FT Worth, TX 76102 | Oil & Gas Operator | Dec 2019 |
| 323 | Monex | | Oil Operator | Apr 1988 |
| 324 | Monexco, Inc. | | Oil Operator | Dec 2003 |
| 325 | Mongrue Oil Company, Inc. | | Oil & Gas Operator | Oct 1999 |
| 326 | Mongrue, Roland, Inc | | Oil & Gas Operator | Mar 1979 |
| 327 | Monroe Gas Associates-1 | | Gas Operator | Mar 2000 |
| 328 | Monroe Gas Associates-2 | | Gas Operator | Mar 2000 |
| 329 | Monroe Gas Joint Venture | | Gas Operator | Sep 2011 |
| 330 | Monroe Well Ser-Amsterdam | | Oil Operator | Dec 1988 |
| 331 | Monroe Well Ser-La Petr Assoc | | Oil Operator | Dec 1988 |
| 332 | Monroe Well Ser-La Petro II | | Oil Operator | Dec 1988 |
| 333 | Monroe Well Ser-New American85 | | Oil Operator | Dec 1988 |
| 334 | Monroe Well Ser-Ocean Petr '84 | | Oil & Gas Operator | Dec 1988 |
| 335 | Monroe Well Ser-Ocean Yacht II | | Oil Operator | May 1989 |
| 336 | Monroe Well Ser-Oceanyacht1985 | | Oil Operator | Dec 1988 |
| 337 | Monroe Well Ser-Riverside 1985 | | Oil Operator | Dec 1988 |
| 338 | Monroe Well Serv-New American | | Oil Operator | Dec 1988 |
| 339 | Monroe Well Serv-Northern La | | Oil Operator | Dec 1988 |
| 340 | Monroe Well Serv-Omega 1985 | | Oil Operator | Dec 1988 |
| 341 | Monroe Well Service | | Oil & Gas Operator | Apr 1998 |
| 342 | Monroe Well Service-Ajk | | Oil Operator | Dec 1988 |
| 343 | Monroe Well Service-Apk | | Oil Operator | Dec 1988 |
| 344 | Monroe Well Service-Beaver1985 | | Oil Operator | Nov 1991 |
| 345 | Monroe Well Service-Broadway | | Oil Operator | Dec 1988 |
| 346 | Monroe Well Service-BWK | | Oil Operator | Dec 1988 |
| 347 | Monroe Well Service-Columbus | | Oil Operator | Dec 1988 |
| 348 | Monroe Well Service-Das | | Oil Operator | Mar 1989 |
| 349 | Monroe Well Service-Derrick | | Oil Operator | Dec 1988 |
| 350 | Monroe Well Service-East End | | Oil Operator | Dec 1988 |
| 351 | Monroe Well Service-Empire | | Oil Operator | Dec 1988 |
| 352 | Monroe Well Service-Energy | | Oil Operator | Dec 1988 |
| 353 | Monroe Well Service-Energy 84 | | Oil Operator | Aug 1989 |
| 354 | Monroe Well Service-Ged | | Oil Operator | Dec 1988 |
| 355 | Monroe Well Service-Gotham | | Oil Operator | Apr 1992 |
| 356 | Monroe Well Service-Gramercy | | Oil Operator | May 1992 |
| 357 | Monroe Well Service-HGC | | Oil Operator | Dec 1988 |
| 358 | Monroe Well Service-Lebo | | Oil Operator | Jun 1989 |
| 359 | Monroe Well Service-Lexington | | Oil Operator | Feb 1989 |
| 360 | Monroe Well Service-Newtown | | Oil Operator | Aug 1990 |
| 361 | Monroe Well Service-Ocean | | Oil Operator | Feb 1989 |
| 362 | Monroe Well Service-Oceanyacht | | Oil Operator | Jan 1989 |
| 363 | Monroe Well Service-Oil City | | Oil Operator | Aug 1992 |
| 364 | Monroe Well Service-Omega | | Oil Operator | Aug 1992 |
| 365 | Monroe Well Service-Par | | Oil Operator | Jan 1990 |
| 366 | Monroe Well Service-Petrol | | Oil Operator | Sep 1992 |
| 367 | Monroe Well Service-Petrovest | | Oil Operator | Dec 1988 |
| 368 | Monroe Well Service-PRG | | Oil Operator | Nov 1990 |
| 369 | Monroe Well Service-Redstone | | Oil Operator | Jul 1989 |
| 370 | Monroe Well Service-RVS | | Oil Operator | Dec 1990 |
| 371 | Monroe Well Service-Shemen | | Oil Operator | Dec 1988 |
| 372 | Monroe Well Service-Shemen1984 | | Oil Operator | Jan 1989 |
| 373 | Monroe Well Service-Shemen1985 | | Oil Operator | Nov 1990 |
| 374 | Monroe Well Service-Sla | | Oil Operator | Mar 1989 |
| 375 | Monroe Well Service-SPD | | Oil Operator | Dec 1988 |
| 376 | Monroe Well Service-SPD 1985 | | Oil Operator | Dec 1988 |
| 377 | Monroe Well Service-TBR | | Oil Operator | Aug 1991 |
| 378 | Monroe Well Service-TG I | | Oil Operator | Oct 1990 |
| 379 | Monroe Well Service-TG II | | Oil Operator | Oct 1990 |
| 380 | Monroe Well Service-TG III | | Oil Operator | Jul 1992 |
| 381 | Monroe Well Service-TG VI | | Oil Operator | Aug 1989 |
| 382 | Monroe Well Service-Tpa 1985 | | Oil Operator | Dec 1990 |
| 383 | Monroe Well Service-Vista | | Oil Operator | Nov 1990 |
| 384 | Monroe Well Service-West End | | Oil Operator | Dec 1988 |
| 385 | Monroe Well Service-York | | Oil Operator | Dec 1988 |
| 386 | Monsanto Company | Indianapolis, IN 46280 | Oil & Gas Operator | Jan 2005 |
| 387 | Monsanto Oil Company | | Oil & Gas Operator | Apr 1986 |
| 388 | Monterey Pipeline Co. | | Oil Operator | Aug 1993 |
| 389 | Monterey Resources LLC | Dallas, TX 75230 | Oil & Gas Operator | Oct 2019 |
| 390 | Moon Operating, Inc. | Longview, TX 75601 | Oil & Gas Operator | Mar 2003 |
| 391 | Moon-Hines-Tigrett Opr Co Inc | | Oil & Gas Operator | Oct 1995 |
| 392 | Moore McCormack Energy, Inc. | | Oil & Gas Operator | Jul 1988 |
| 393 | Moore Oil & Gas-Marion Corp. | | Oil & Gas Operator | Nov 1986 |
| 394 | Moore&Munger Hydrocarbons Inc | | Oil Operator | May 1987 |
| 395 | Mooringsport Energy Prod Corp | | Oil & Gas Operator | Oct 1994 |
| 396 | Mooringsport Energy Trans Corp | | Oil Operator | Apr 1990 |
| 397 | Mor-Co Investments, Inc. | | Gas Operator | Feb 1994 |
| 398 | Moran Exploration, Inc. | | Oil & Gas Operator | Jan 1985 |
| 399 | Moran Oil Co., Inc. | | Oil & Gas Operator | Aug 2009 |
| 400 | Moransco Energy Corporation | Kilgore, TX 75663 | Oil & Gas Operator | Mar 2025 |