| 301 | Kelly Operating Company | | Oil & Gas Operator | Oct 1991 |
| 302 | Kem Ventures, LP | Katy, TX 77450 | Oil & Gas Operator | Dec 2025 |
| 303 | Kenai Oil & Gas Inc | | Oil & Gas Operator | Jun 1987 |
| 304 | Kennedy & Mitchell | Woodward, OK 73802 | Oil & Gas Operator | Dec 1988 |
| 305 | Kennedy George C | Upton, WY 82730 | Oil & Gas Operator | Oct 2018 |
| 306 | Kennedy Oil | Gillette, WY 82716 | Oil & Gas Operator | Jan 2026 |
| 307 | Kerr-McGee Corporation | Dallas, TX 75380 | Oil & Gas Operator | Sep 2025 |
| 308 | Kestrel Energy Inc | Lakewood, CO 80401 | Oil & Gas Operator | Jan 2008 |
| 309 | Kirkwood W C | Casper, WY 82602 | Oil & Gas Operator | May 2005 |
| 310 | Kissack Resources. LLC | | Oil & Gas Operator | Jan 2026 |
| 311 | Kissack Water & Oil Service Inc | Rozet, WY 82727 | Oil & Gas Operator | Jan 2026 |
| 312 | Kissinger Petroleum Corp | | Oil & Gas Operator | Nov 1983 |
| 313 | Klabzuba Oil & Gas Inc | Denver, CO 80202 | Oil & Gas Operator | Aug 2012 |
| 314 | L & J Operating Inc | Gillette, WY 82718 | Oil & Gas Operator | Aug 2016 |
| 315 | L & R Drilling Company | Belle Fourche, SD 57717 | Oil & Gas Operator | Dec 1999 |
| 316 | L B Industries Inc | Englewood, CO 80112 | Oil & Gas Operator | Jun 2003 |
| 317 | Ladd & Lukowicz | | Oil & Gas Operator | May 1983 |
| 318 | Laguna Petroleum Company | Casper, WY 82601 | Oil & Gas Operator | Dec 1982 |
| 319 | Lance Oil & Gas Company Inc | Kirtland, NM 87417 | Oil & Gas Operator | Mar 2013 |
| 320 | Langley Energy | Euless, TX 76040 | Gas Operator | Jan 2016 |
| 321 | Lario Oil & Gas Company | Odessa, TX 79762 | Oil & Gas Operator | Mar 2026 |
| 322 | Lasmo Energy Corporation | Tulsa, OK 74136 | Oil & Gas Operator | Jan 2024 |
| 323 | Lear Petroleum Exploration | | Oil & Gas Operator | Jul 2013 |
| 324 | Leclair-Westwood Inc | | Oil & Gas Operator | Mar 1982 |
| 325 | Legacy Reserves Operating LP | Denver, CO 80201 | Oil & Gas Operator | Mar 2026 |
| 326 | Levinson Partners Corporation | Denver, CO 80202 | Oil & Gas Operator | Jul 1995 |
| 327 | Liberty Resources Management Co LLC | Denver, CO 80202 | Oil & Gas Operator | Jan 2026 |
| 328 | Loil Oil LLC | Golden, CO 80402 | Oil & Gas Operator | Jan 2026 |
| 329 | Long Trust The | Kilgore, TX 75663 | Oil & Gas Operator | Aug 2008 |
| 330 | Loral Operating LLC | Sheridan, WY 82801 | Gas Operator | Apr 2011 |
| 331 | Louisiana Land & Exploration Co. | Houston, TX 77210 | Oil & Gas Operator | Sep 2013 |
| 332 | Low D J | Littleton, CO 80127 | Oil Operator | Dec 1999 |
| 333 | Lowry Exploration Inc | Tulsa, OK 74119 | Oil & Gas Operator | Dec 2025 |
| 334 | Luff Exploration | Denver, CO 80203 | Oil & Gas Operator | Dec 2006 |
| 335 | M & K Oil Company LLC | Gillette, WY 82716 | Oil & Gas Operator | Jan 2026 |
| 336 | Mack Energy Corporation | Artesia, NM 88211 | Oil & Gas Operator | Jan 2026 |
| 337 | Main Energy, Inc. | Houston, TX 77079 | Oil & Gas Operator | May 2009 |
| 338 | Majestic Petroleum Operations Inc | Story, WY 82842 | Gas Operator | Mar 2007 |
| 339 | Mallon Oil Company | Denver, CO 80202 | Oil & Gas Operator | Jun 2005 |
| 340 | Manx Oil Corporation | Casper, WY 82601 | Oil & Gas Operator | Jun 2010 |
| 341 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Jan 2026 |
| 342 | Marlin Oil Company LLC | Gillette, WY 82718 | Oil & Gas Operator | Mar 2023 |
| 343 | Marmik Oil Company | El Dorado, AR 71730 | Oil & Gas Operator | Jan 2015 |
| 344 | Martens & Peck Operating Co | | Gas Operator | Feb 1997 |
| 345 | Martens & Peck Production Co | Denver, CO 80222 | Oil & Gas Operator | Feb 1997 |
| 346 | Matrix Production Company | Sugar Land, TX 77478 | Oil & Gas Operator | Dec 2025 |
| 347 | Maxim Drilling & Expl Inc | Gillette, WY 82717 | Oil & Gas Operator | Jan 2026 |
| 348 | Maximus Operating, LTD. | Kilgore, TX 75663 | Oil & Gas Operator | Mar 2026 |
| 349 | Mbi Oil & Gas LLC | Dickinson, ND 58601 | Oil & Gas Operator | Jan 2026 |
| 350 | McAdams Roux & Associates | Denver, CO 80202 | Oil & Gas Operator | Dec 1999 |
| 351 | McClure Enterprises | Recluse, WY 82725 | Oil & Gas Operator | Jul 2025 |
| 352 | McGuire John C | Gillette, WY 82717 | Oil & Gas Operator | Oct 2005 |
| 353 | McKenzie Production Company | Houston, TX 77063 | Oil & Gas Operator | May 1995 |
| 354 | MCL 1 Oil & Gas Wyoming LLC | Minneapolis, MN 55402 | Oil & Gas Operator | Jul 2018 |
| 355 | McMahon-Bullington LP | Wichita Falls, TX 76307 | Oil & Gas Operator | Apr 2009 |
| 356 | McMurry Oil LLC | Denver, CO 80202 | Oil & Gas Operator | Dec 2004 |
| 357 | McRae & Henry LTD | Golden, CO 80401 | Oil & Gas Operator | May 2022 |
| 358 | MDS Energy Development LLC | | Oil & Gas Operator | Jan 2026 |
| 359 | Medallion Exploration | Holladay, UT 84117 | Oil & Gas Operator | Dec 2015 |
| 360 | Medallion Production Company | Tulsa, OK 74103 | Oil & Gas Operator | May 1997 |
| 361 | Medicine Bow Operating Company | Houston, TX 77002 | Oil & Gas Operator | Apr 2014 |
| 362 | Mega Energy LLC | Gillette, WY 82718 | Gas Operator | Jan 2026 |
| 363 | Merit Energy Company | Dallas, TX 75240 | Oil & Gas Operator | Mar 2026 |
| 364 | Meritage Energy Partners LLC | Denver, CO 80202 | Oil & Gas Operator | Dec 2005 |
| 365 | Merrimac Oil & Gas LLC | Houston, TX 77054 | Gas Operator | Dec 2008 |
| 366 | Merrion Oil & Gas Corp | Farmington, NM 87401 | Oil & Gas Operator | Jan 2026 |
| 367 | Methane Productions Inc | Recluse, WY 82725 | Oil & Gas Operator | Apr 2007 |
| 368 | Meyer Douglas P | Longmont, CO 80501 | Oil & Gas Operator | Aug 2006 |
| 369 | Mi3 Energy LLC | | Oil & Gas Operator | Jan 2026 |
| 370 | Michigan-Wisconsin Pipe Line Co | | Oil & Gas Operator | Dec 1983 |
| 371 | Mid-Con Energy Operating, LLC | Tulsa, OK 74136 | Oil & Gas Operator | Jan 2026 |
| 372 | Midgard Energy Company | The Woodlands, TX 77380 | Oil & Gas Operator | Dec 2014 |
| 373 | Minnelusa Oil LLC | Temecula, CA 92589 | Oil Operator | Feb 2002 |
| 374 | Mitchell Energy Corp | Houston, TX 77002 | Oil & Gas Operator | Aug 2013 |
| 375 | Mitchell M J | | Oil & Gas Operator | Jan 1983 |
| 376 | Mobil Expl & Producing North America Inc | | Oil & Gas Operator | Nov 1986 |
| 377 | Monahan Rex | Sterling, CO 80751 | Oil & Gas Operator | Jun 2002 |
| 378 | Moncrief W A Jr | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 2026 |
| 379 | Monsanto Company | Indianapolis, IN 46280 | Oil & Gas Operator | Jan 2005 |
| 380 | Montex Drilling Company LLC | Fort Worth, TX 76102 | Oil & Gas Operator | Mar 2026 |
| 381 | Montex Exploration | Sugarland, TX 77478 | Oil Operator | Apr 2003 |
| 382 | Mosbacher Production Co. | Houston, TX 77001 | Oil & Gas Operator | Aug 1984 |
| 383 | Mountain Hawk Energy LLC | Athens, TX 75751 | Gas Operator | Jan 2015 |
| 384 | MTG Operating Inc | Ridgeland, MS 39158 | Gas Operator | Apr 2011 |
| 385 | Mull Drilling Company | Wichita, KS 67206 | Oil & Gas Operator | Dec 2025 |
| 386 | Murphy Oil USA, Inc. | New Orleans, LA 70161 | Oil & Gas Operator | Jan 1993 |
| 387 | Murphy Sheldon L & Loretta | Newcastle, WY 82701 | Oil & Gas Operator | Jan 2026 |
| 388 | MWJ Producing Company | Midland, TX 79701 | Oil & Gas Operator | Jul 1998 |
| 389 | Nadel And Gussman Rockies, LLC | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2012 |
| 390 | Nance Petroleum Corporation | Billings, MT 59103-7168 | Oil & Gas Operator | Nov 2007 |
| 391 | National Energy Group Inc | Dallas, TX 75206 | Oil & Gas Operator | Sep 2014 |
| 392 | National Oil Company | Garden City, KS 67846 | Oil & Gas Operator | Jun 2024 |
| 393 | National Pride Operating | Parker, CO 80134 | Oil & Gas Operator | Dec 2017 |
| 394 | Natomas North America Inc | | Oil & Gas Operator | Aug 1993 |
| 395 | Navigation Powder River LLC | Houston, TX 77024 | Oil & Gas Operator | Jan 2026 |
| 396 | Neward Corporation | FT. Worth, TX 76102 | Oil & Gas Operator | Dec 1997 |
| 397 | Newport Gas Partners LLC | Gillette, WY 82716 | Oil & Gas Operator | Oct 2025 |
| 398 | Nicolaysen G G Jr | | Oil & Gas Operator | Dec 1995 |
| 399 | Nicor Exploration | | Oil Operator | Jul 1993 |
| 400 | Nicor Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Jun 1993 |