| 2101 | MDMP | MIDMAR TRANSPORTATION | | | SCAC4 |
| 2102 | MDMQ | MDM INDUSTRIES INC | | | SCAC4 |
| 2103 | MDMR | MEDITERRANE | | | SCAC4 |
| 2104 | MDMS | MODERN MOVING & STORAGE | | | SCAC4 |
| 2105 | MDMT | MERIDIAN MANUFACTURING GROUP CANADA | | | SCAC4 |
| 2106 | MDMU | MIDMAC CONTRACTING INTERNATIONAL CO | | | SCAC4 |
| 2107 | MDMV | MERCHA | | | SCAC4 |
| 2108 | MDMW | MEAL AND MORE INC | | | SCAC4 |
| 2109 | MDMY | MR D'S MOVING COMPANY | | | SCAC4 |
| 2110 | MDN | Meridiana Air, SA | IATA: RH, Callsign: Meridiana Air, Ceased operations on 16 October 1992. | E | AVCODES |
| 2111 | MDN | Meridian+, NP AGP, LLC | | RUS | AVCODES |
| 2112 | MDN | Mcdan Aviation San Marino S.r.l. | Callsign: Macdan, | RSM | AVCODES |
| 2113 | MDN | Mudan Airlines | | | ICAO1 |
| 2114 | MDNB | MADDEN LTD | | | SCAC4 |
| 2115 | MDND | MCDONALD TRUCKING | | | SCAC4 |
| 2116 | MDNJ | MIDNIGHT OIL CO | | | SCAC4 |
| 2117 | MDNL | MERIDIAN LINE | | | SCAC4 |
| 2118 | MDNM | MCDANNELL OIL | | | SCAC4 |
| 2119 | MDNN | MIDNIGHT TRANSPORT | | | SCAC4 |
| 2120 | MDNP | MARQUIS, DANNY & SON TRANSPORT | | | SCAC4 |
| 2121 | MDNR | MUSICAL DEL NORTE SA DE CV | | | SCAC4 |
| 2122 | MDNV | METAL DESIGN NIAGARA | | | SCAC4 |
| 2123 | MDNW | MADISON INTERMODAL LLC | | | SCAC4 |
| 2124 | MDNY | MIDNIGHT TRUCKING | | | SCAC4 |
| 2125 | MDO | Varty Pacific Airlines S.R.L. | Callsign: Varty, | KZ | AVCODES |
| 2126 | MDO | Shervbery | Callsign: Murman, | GE | AVCODES |
| 2127 | MDO | Mediterranean Aviation Operations Company Ltd. | IATA: 5M, Callsign: Kuda, Name changed to Mediterranean Aviation Operations Company Ltd. d/b/a MedOps | M | AVCODES |
| 2128 | MDO | Mediterranean Aviation Operations Company Ltd. d/b/a MedOps | IATA: 5M, Callsign: Kuda, Name changed from Mediterranean Aviation Operations Company Ltd. | M | AVCODES |
| 2129 | MDO | Mel Air Limited | IATA: 5M, Callsign: Kuda, Name changed from Mediterranean Aviation Operations Company Ltd. d/b/a MedOps and previously from Mediterranean Aviation Operations Company Ltd. | M | AVCODES |
| 2130 | MDOA | MODA TRANSPORT | | | SCAC4 |
| 2131 | MDOD | MUDANZAS GOU S A DE C V | | | SCAC4 |
| 2132 | MDOF | MEIER DUITSMAN OIL COMPANY INC | | | SCAC4 |
| 2133 | MDOL | M & D TRANSPORT LLC | | | SCAC4 |
| 2134 | MDOQ | MCDERMOTT INC | | | SCAC4 |
| 2135 | MDOR | MARTRANS ( DIV OF TFI 3 TRANSPORT L | | | SCAC4 |
| 2136 | MDOS | MACTOOLS DIVISION OF STANLEYWORKS | | | SCAC4 |
| 2137 | MDOT | Maryland Department of Transportation | | USA | TRAFFIC |
| 2138 | MDOU | Qingdao MMD Offshore Manufacture Co.,Ltd. | | PRC | BIC |
| 2139 | MDOW | MIDOCEAN (IOM) LTD | | | SCAC4 |
| 2140 | MDP | Medallion Air | Founded in 2009. Merged into Ten Airways in July 2013. | RO | AVCODES |
| 2141 | MDP | Mexican Pacific R.R. Co., Inc. (transferred to Ferrocarriles Nacionales de Mexico) | eliminated 10/1988 | | NAKINA |
| 2142 | MDP | Mexican Pacific R.R. Co., Inc. (Ferrocarril Mexicano del Pacifico, S.A.) | 1/1975-1/1980 | | NAKINA |
| 2143 | MDP | Mexican Pacific R.R. Co., Inc. (Ferrocarril Mexicano del Pacifico, S.A.) | 1/75-1/80 | | NRHS |
| 2144 | MDP | Mexican Pacific R.R. Co., Inc. (transferred to Ferrocarriles Nacionales de Mexico) | eliminated 10/88 | | NRHS |
| 2145 | MDP | MEXICAN PACIFIC RAILROAD (FERROCARRIL MEXICANO DEL PACIFICO, SA) | | | PWRC |
| 2146 | MDP | Mexican Pacific Railroad (Ferrocarril Mexicano del Pacifico) | | | RSRV |
| 2147 | MDPB | MODERN DISPOSAL SERVICES INC | | | SCAC4 |
| 2148 | MDPD | MICELI DAIRY PRODUCTS INC | | | SCAC4 |
| 2149 | MDPE | MED PACIFIC EXPRESS | | | SCAC1 |
| 2150 | MDPE | MARTINEZ DE LA PENA, JULIO CESAR | | | SCAC4 |
| 2151 | MDPF | MID-AMERICA CARRIER GROUP CORPORATI | | | SCAC4 |
| 2152 | MDPI | McCARTHY, DAVID P | | | SCAC1 |
| 2153 | MDPJ | METAMORFOSIS DOCUMENTATION PROJECT | | | SCAC4 |
| 2154 | MDPK | MID-PLAINS IMPLEMENTS LTD | | | SCAC4 |
| 2155 | MDPL | MADERA PALLETS&TRANSPORTS | | | SCAC1 |
| 2156 | MDPL | MADERA PALLETS & TRANSPORT | | | SCAC4 |
| 2157 | MDPM | MID-ATLANTIC PETROLEUM TRANSPORT LL | | | SCAC4 |
| 2158 | MDPN | MINNESOTA DEPARTME | | | SCAC4 |
| 2159 | MDPO | MEDINA TRANSPORT, INC. | | | SCAC1 |
| 2160 | MDPO | MCDONOUGH PROJECT SERVICES LP | | | SCAC4 |
| 2161 | MDPO | Městský dopravni podnik Opava | City: Opava | CZ | TRAFFIC |
| 2162 | MDPP | MDP TRANSPORTATION | | | SCAC4 |
| 2163 | MDPR | M & D PROPERTIES LTD | | | SCAC4 |
| 2164 | MDPT | MID-PACIFIC TRANSPORTATION INC | | | SCAC4 |
| 2165 | MDPU | MODERN SHIPPING LINES CO LTD | | HK | BIC |
| 2166 | MDPV | MIDWEST ASPHALT CORP | | | SCAC4 |
| 2167 | MDPY | MODIPO AUTO LLC | | | SCAC4 |
| 2168 | MDQN | MEDLINE SHIPPING LTD. | | | SCAC4 |
| 2169 | MDQO | MODERN MOLD 2004 INC | | | SCAC4 |
| 2170 | MDQP | MCDERMOTT TRANSPORTATION INC | | | SCAC4 |
| 2171 | MDR | Compania Mexicana de Aeroplanos, S.A. | Callsign: Aeroplanos, | MEX | AVCODES |
| 2172 | MDR | Compania Mexicana De Aeroplanos | | | ICAO1 |
| 2173 | MDR | Kansas City Southern Ry. Co. | added 7/1994; 7/2000-7/2005 | | NAKINA |
| 2174 | MDR | MidLouisiana Rail Corp. | added 1/1988; 1/1994; eliminated 7/1994 | | NAKINA |
| 2175 | MDR | MidLouisiana Rail Corp. | added 1/88; 1/94; eliminated 7/94 | | NRHS |
| 2176 | MDR | Kansas City Southern Ry. Co. | added 7/94; 7/2000 | | NRHS |
| 2177 | MDR | KANSAS CITY SOUTHERN RAILWAY COMPANY {MIDLOUSIANA RAIL CORP.] | | | PWRC |
| 2178 | MDR | Kansas City Southern Railway | | | RSRV |
| 2179 | MDRA | M & D RAPIDS TRUCKING | | | SCAC4 |
| 2180 | MDRD | MACDOUGALL, ROBERT BRYDEN | | | SCAC4 |
| 2181 | MDRF | MEADOW RIDGE FARMS INC | | | SCAC4 |
| 2182 | MDRG | MEDINA ROJAS, MARGARITA | | | SCAC4 |
| 2183 | MDRI | MDR GLOBAL LOGISTICS LLC | | | SCAC4 |
| 2184 | MDRJ | MDR TRANSPORTATION LIMITED | | | SCAC4 |
| 2185 | MDRM | MARITIME DREAM SA PANAMA | | | SCAC4 |
| 2186 | MDRN | MODERN TRANSFER CO INC | | | PWRC |
| 2187 | MDRO | S.E.L. MADURO | | | PWRC |
| 2188 | MDRP | M & D TRANSPORT | | | SCAC4 |
| 2189 | MDRR | MADORE ENTERPRISES LTD | | | SCAC4 |
| 2190 | MDRS | MAQUILADORA AUREA S A DE C V | | | SCAC4 |
| 2191 | MDRT | MDR TRANSPORTATION LIMITED | | | SCAC4 |
| 2192 | MDRV | MAD RIVER TRANSPORTATION INC | | | SCAC4 |
| 2193 | MDRW | MILLER, DOLAN R | | | SCAC4 |
| 2194 | MDRX | MDRC-1 LLC | added 10/2003; eliminated 4/2004; 7/2005 (not listed) | | NAKINA |
| 2195 | MDRX | Midland Refining Co. (Skelly Oil Co.) | 7/1923 | | NAKINA |
| 2196 | MDRX | The Midland Refining Co. | 8/1920 | | NAKINA |
| 2197 | MDRX | *SKELLY OIL CO. [MIDLAND REFINING CO.] | | | PWRC |
| 2198 | MDRX | +MDRC-1 LLC | | | PWRC |
| 2199 | MDRX | MDRC-1 LLC | | | SCAC4 |
| 2200 | MDRY | Madison Ry. Co., Inc. | added 1/1978; eliminated 1/1979 | | NAKINA |
