| 4501 | MKCO | MORRISON KNUDSEN CORPORATION | | | PWRC |
| 4502 | MKCO | M K TRUCKING INC | | | SCAC4 |
| 4503 | MKCS | MILWAUKEE-KANSAS CITY S. JOINT AGENCY | | | PWRC |
| 4504 | MKCS | MUNKITTRICK TRANSPORT INC | | | SCAC4 |
| 4505 | MKCT | MAESTRA LINE TRUCKING | | | SCAC4 |
| 4506 | MKCX | Morrison Knudsen Corp. | 7/2000-7/2005 (not listed) | | NAKINA |
| 4507 | MKCX | Michigan Chemical Co. | 7/1923 | | NAKINA |
| 4508 | MKCX | Morrison Knudsen Corp. | Jul-00 | | NRHS |
| 4509 | MKCX | *MICHIGAN CHEMICAL CO. | | | PWRC |
| 4510 | MKCX | +MORRISON KNUDSEN CORPORATION | | | PWRC |
| 4511 | MKCX | Morrison Knudsen Corporation | | | RSRV |
| 4512 | MKCX | MORRISON KNUDSEN CORPORATION | | | SCAC4 |
| 4513 | MKCY | MACKENZIE | | | SCAC4 |
| 4514 | MKD | Mat Airways | Callsign: Matairways, Founded in March 2009. Ceased operations in 2011. | MK | AVCODES |
| 4515 | MKD | MAT Airways | Real: MKD, 6F | MK | TRAFFIC |
| 4516 | MKDA | MEEKER, DAVE AUTO INC | | | SCAC4 |
| 4517 | MKDG | MAKUR DESIGNS INC | | | SCAC4 |
| 4518 | MKDI | MEK TRUCKING | | | SCAC4 |
| 4519 | MKDN | MCKAY, DON TRUCKING LIMITED | | | SCAC4 |
| 4520 | MKDR | MARKDA | | | SCAC4 |
| 4521 | MKDS | MIKADE DELIVERY SERVICE INC | | | SCAC4 |
| 4522 | MKDT | MKD INTERNATIONAL INC | | | SCAC4 |
| 4523 | MKE | PT. Megantara Air | IATA: 9M, Callsign: Megantara, IATA Prefix: 824, Founded in 2007. Ceased operations in May 2009. Designator reinstated by IATA. | RI | AVCODES |
| 4524 | MKEA | MEIKLE AUTOMATION INC | | | SCAC4 |
| 4525 | MKEB | MCKEE BROTHERS OIL CORP | | | SCAC4 |
| 4526 | MKEC | MIKEN CARTAGE INC | | | SCAC4 |
| 4527 | MKED | MACKINNON, E D TRUCKING LTD | | | SCAC4 |
| 4528 | MKEE | MAKSTEE | | | SCAC4 |
| 4529 | MKEI | MARKETEC TRANSPORT INCORPORATED | | | SCAC4 |
| 4530 | MKEP | MALKE ENTERPRISES LTD | | | SCAC4 |
| 4531 | MKER | MIDKNIGHT EXPRESS INC | | | SCAC4 |
| 4532 | MKERT | MÁV KERT Kft. | | HU | VKM |
| 4533 | MKES | MIKES INC | | | SCAC4 |
| 4534 | MKET | MARKET TRANSPORT, LTD | | | SCAC1 |
| 4535 | MKFB | MAR-KO FREIGHT SERVICES | | | SCAC4 |
| 4536 | MKFC | MEAKIN FOREST ENTERPRISES INC | | | SCAC4 |
| 4537 | MKFM | MCKEE FARM TECHNOLOGIES INC | | | SCAC4 |
| 4538 | MKFN | MAKS FREIGHT INC | | | SCAC4 |
| 4539 | MKFP | MIDKIFF COOP | | | SCAC4 |
| 4540 | MKFQ | MK FREIGHT BROKER INC | | | SCAC4 |
| 4541 | MKFX | Century Rail Enterprises, Inc. | 7/2005 (not listed) | | NAKINA |
| 4542 | MKFX | CENTURY RAIL ENTERPRISES, INC. | | | PWRC |
| 4543 | MKFX | Century Rail Enterprises | | | RSRV |
| 4544 | MKG | Mekong Aviation JSC (Air Mekong) | IATA: P8, Callsign: Air Mekong, IATA Prefix: 819, Ceased operations on 01 March 2013. AOC revoked January 2015. ICAO callsign changed from Mekong | VN | AVCODES |
| 4545 | MKG | Mekong Aviation JSC (Air Mekong) | IATA: P8, Callsign: Mekong, IATA Prefix: 819, ICAO callsign changed to Air Mekong | VN | AVCODES |
| 4546 | MKGA | MK GAS CO | | | SCAC4 |
| 4547 | MKGB | MAVERICK TRUCKING INC | | | SCAC4 |
| 4548 | MKGE | MUSICK TRUCKING CO | | | SCAC4 |
| 4549 | MKGF | MAK LOGISTICS LLC | | | SCAC4 |
| 4550 | MKGH | MINERAL KING TRANSPORTATION LLC | | | SCAC4 |
| 4551 | MKGL | MCCLAIN, TIM TRUCKING | | | SCAC4 |
| 4552 | MKGM | M A C TRUCKING LTD | | | SCAC4 |
| 4553 | MKGN | MIKES GLASS & MIRROR CO INC | | | SCAC4 |
| 4554 | MKGO | MIMI TRUCKING LLC | | | SCAC4 |
| 4555 | MKGS | MARKET LOGISTICS (DIV OF MARKET TRA | | | SCAC4 |
| 4556 | MKGU | GATI COAT TO COAST | | | SCAC4 |
| 4557 | MKGV | M A S TRUCKING SERVICES CORP | | | SCAC4 |
| 4558 | MKGX | North American Car Corp. | added 10/1960; 4/1961-1/1975; eliminated 10/1979 | | NAKINA |
| 4559 | MKGX | North American Car Corp. | added 10/60; 4/61-1/75 | | NRHS |
| 4560 | MKGX | NORTH AMERICAN CAR CORP. | | | PWRC |
| 4561 | MKH | Air Marrakech Service | Callsign: Air Marrakech, | MA | AVCODES |
| 4562 | MKH | Air Marrakech Service | | | ICAO1 |
| 4563 | MKHC | MKH TRANSPORTATION INC | | | SCAC4 |
| 4564 | MKHI | MIKASHA INC | | | SCAC4 |
| 4565 | MKHK | MASSEY | | | SCAC4 |
| 4566 | MKHL | MCGEE, KEN HOLDINGS INC | | | SCAC4 |
| 4567 | MKHN | MK HEAVY TRANSPORT LLC | | | SCAC4 |
| 4568 | MKHO | MARKETHOUS | | | SCAC4 |
| 4569 | MKHT | MIKHAIL TRUCKING LLC | | | SCAC4 |
| 4570 | MKI | Mk Flugfielagid EHF | Callsign: Kilo Ice, | IS | AVCODES |
| 4571 | MKIA | M T K INC | | | SCAC4 |
| 4572 | MKIG | MTJ TRUCKING | | | SCAC4 |
| 4573 | MKIK | MANKOWSK | | | SCAC4 |
| 4574 | MKIT | MOBILE KITCHENS CANADA | | | SCAC4 |
| 4575 | MKIX | Morrison Knudsen Corp. | 7/2000-7/2005 (not listed) | | NAKINA |
| 4576 | MKIX | M-K Railroad Equipment Leasing Co., Inc. | added 1/1976; 1/1980; eliminated 4/1989; 1/1994 (not listed) | | NAKINA |
| 4577 | MKIX | Morrison-Knudsen Railroad Equipment Leasing Co., Inc. | added 10/1975; eliminated 1/1976 | | NAKINA |
| 4578 | MKIX | Morrison-Knudsen Co., Inc. | added 10/1971; 1/1975; eliminated 10/1975 | | NAKINA |
| 4579 | MKIX | Marshall Kirby & Co., Inc. (Merchants Despatch, Inc.) | 7/1935 | | NAKINA |
| 4580 | MKIX | Morrison-Knudsen Co., Inc. | added 10/71; 1/75 | | NRHS |
| 4581 | MKIX | M-K Railroad Equipment Leasing Co., Inc. | 1/80; eliminated 4/89; 1/94 | | NRHS |
| 4582 | MKIX | Morrison Knudsen Corp. | Jul-00 | | NRHS |
| 4583 | MKIX | MORRISON KNUDSEN CORPORATION [M-K RAILROAD EQUIPMENT LEASING CO.] | | | PWRC |
| 4584 | MKIX | M-K Railroad Equipment Leasing (Morrison Knudsen Corporation) | | | RSRV |
| 4585 | MKIX | MORRISON KNUDSEN CORPORATION | | | SCAC4 |
| 4586 | MKIX | Morrison Knudsen Corp. | | USA | TRAFFIC |
| 4587 | MKK | Malaya Aviatsia Dona | Callsign: Aerokey, | RUS | AVCODES |
| 4588 | MKK | Malaya Aviatsia Dona | | | ICAO1 |
| 4589 | MKKC | MORGAN, KEITH TRUCKING INC | | | SCAC4 |
| 4590 | MKKG | MACK TRUCKING VIOLA INC | | | SCAC4 |
| 4591 | MKKN | MK TRUCKING TRANS | | | SCAC4 |
| 4592 | MKKQ | MIKES TRUCK & TRACTOR INC | | | SCAC4 |
| 4593 | MKL | McCall Aviation, Inc. | IATA: S6, Callsign: Mccall, | USA | AVCODES |
| 4594 | MKL | McCall Aviation, Inc. | Callsign: Mccall, IATA Designator S6 recalled. | USA | AVCODES |
| 4595 | MKL | McCall Aviation | | | ICAO1 |
| 4596 | MKLA | MCALISTER TRANSPORTATION LLC | | | SCAC4 |
| 4597 | MKLB | M & K LOGISTICS LLC | | | SCAC4 |
| 4598 | MKLJ | MARKUS LOGISTICS INC | | | SCAC4 |
| 4599 | MKLL | MCKELL TRANSPORTATION REGD | | | SCAC4 |
| 4600 | MKLM | MAJOR KAT LEASING INC | | | SCAC4 |
