| 1 | MRX | Hermen's Markair Express | Callsign: Speedmark, | USA | AVCODES |
| 2 | MRX | North American Car Corp. | added 7/1955; 10/1957-7/1965; eliminated 10/1966; 10/1966 (not listed); 4/1970-1/1975 | | NAKINA |
| 3 | MRX | Mather Stock Car Co. | added 7/1954; 7/1954; eliminated 7/1955 | | NAKINA |
| 4 | MRX | Morrell Refrigerator Line | eliminated 7/1954 | | NAKINA |
| 5 | MRX | Morrell Refrigerator Line (T.H. Foster, Trustee) | 7/1937-1/1952 | | NAKINA |
| 6 | MRX | Morrell Refrigerator Car Co. (Dissolved) | 7/1930-7/1935 | | NAKINA |
| 7 | MRX | Morrell Refrigerator Line | 8/1920-7/1923 | | NAKINA |
| 8 | MRX | Morrell Refrigerator Car Co. (Dissolved) | Apr-38 | | NRHS |
| 9 | MRX | Morrell Refrigerator Line (T.H. Foster, Trustee) | Jan-52 | | NRHS |
| 10 | MRX | Mather Stock Car Co. | eliminated 7/55 | | NRHS |
| 11 | MRX | North American Car Corp. | added 7/55; 10/57-7/65; eliminated 10/66; 4/70-1/75 | | NRHS |
| 12 | MRX | *MORRELL REFRIGERATOR LINE [JOHN MORRELL & CO.] (NCCO [MATHER STOCK CAR CO.]) | | | PWRC |
| 13 | MRX | *MIDLANDS RAILROAD | | | PWRC |
| 14 | MRXB | M & R TRANSPORT INC | | | SCAC4 |
| 15 | MRXC | MARGAREE EXCAVA | | | SCAC4 |
| 16 | MRXG | MAR-TEX SHIPPING & CHARTERING AGENC | | | SCAC4 |
| 17 | MRXI | MUROX INDUSTRIES LTD | | | SCAC4 |
| 18 | MRXK | MUNRO TRANSPORT LTD | | | SCAC4 |
| 19 | MRXL | MATRIX INTERNATIONAL LOGISTICS INC | | | SCAC4 |
| 20 | MRXP | MARX TRANSPORT INC | | | SCAC4 |
| 21 | MRXR | MOORES TRANSPORT LLC | | | SCAC4 |
| 22 | MRXS | MATRIX SCALE SERVICE INC | | | SCAC4 |
| 23 | MRXT | MOLNAR TRANSPORT INC | | | SCAC4 |
| 24 | MRXW | MARTINS REFRIGERATED EXPRESS INC | | | SCAC4 |
| 25 | MRXY | MORIN TRANSFER | | | SCAC4 |
