| 1 | MRR | Northwest Seaplanes, Inc. d/b/a San Juan Airlines | IATA: 2G, Callsign: Mariner, Name changed to West Isle Air, Inc. d/b/a San Juan Airlines. Name changed from Northwest Seaplanes, Inc. | USA | AVCODES |
| 2 | MRR | Northwest Seaplanes, Inc. | IATA: 2G, Callsign: Mariner, Name changed to Northwest Seaplanes, Inc. d/b/a San Juan Airlines | USA | AVCODES |
| 3 | MRR | West Isle Air, Inc. d/b/a San Juan Airlines | IATA: 2G, Callsign: Mariner, Name changed from Northwest Seaplanes, Inc. d/b/a San Juan Airlines. Previous name changed from Northwest Seaplanes, Inc. | USA | AVCODES |
| 4 | MRR | West Isle Air, Inc. | Callsign: Mariner, Name changed from West Isle Air, Inc. d/b/a San Juan Airlines and previously from Northwest Seaplanes, Inc. d/b/a San Juan Airlines. Previous name changed from Northwest Seaplanes, Inc. | USA | AVCODES |
| 5 | MRR | San Juan Airlines | IATA: 2G* | | ICAO1 |
| 6 | MRR | The Carolina Southern R.R. Co. | added 4/1996; 7/2000; eliminated 10/2002; 7/2005 | | NAKINA |
| 7 | MRR | Mid Atlantic R.R. Co., Inc. | added 7/1988; 1/1994; eliminated 4/1996 | | NAKINA |
| 8 | MRR | Mid Atlantic R.R. Co., Inc. | added 7/88; 1/94; eliminated 4/96 | | NRHS |
| 9 | MRR | The Carolina Southern R.R. Co. | added 4/96; 7/2000 | | NRHS |
| 10 | MRR | CAROLINA SOUTHERN RAILROAD [MID ATLANTIC RAILROAD CO., INC.] | | | PWRC |
| 11 | MRR | Mid Atlantic Railroad (Carolina Southern Railroad) | | | RSRV |
| 12 | MRR | Mid Atlantic R.R. Co., Inc. | | USA | TRAFFIC |
| 13 | MRRC | MOORE, R C INC | | | SCAC4 |
| 14 | MRRD | MORRISSEY | | | SCAC4 |
| 15 | MRRH | MORRISONS TRUCKING | | | SCAC4 |
| 16 | MRRL | MERCURY LINES | | | SCAC4 |
| 17 | MRRO | MARRAN OIL LLC | | | SCAC4 |
| 18 | MRRR | MORRIS TRANSPORTATION SYSTEMS INC | | | SCAC4 |
| 19 | MRRS | MORRISON EXPRESS CORPORATION (USA) | | | SCAC4 |
| 20 | MRRX | Murphy Road Recycling LLC | added 1/2004; 7/2005 | | NAKINA |
| 21 | MRRX | General Electric Railcar Services Corp. | added 1/1984; 1/1994; eliminated 10/1994 | | NAKINA |
| 22 | MRRX | North American Car Corp. | added 7/1955; 10/1957-1/1980; eliminated 1/1984 | | NAKINA |
| 23 | MRRX | Mather Refrigerator Express (Mather Stock Car Co.) | 7/1930-7/1954; eliminated 7/1955 | | NAKINA |
| 24 | MRRX | Mather Refrigerator Express (Mather Horse & Stock Car Co.) | 8/1920-7/1923 | | NAKINA |
| 25 | MRRX | Mather Refrigerator Express (Mather Stock Car Co.) | Apr-38 | | NRHS |
| 26 | MRRX | Mather Stock Car. Co. | 1/52; eliminated 7/55 | | NRHS |
| 27 | MRRX | North American Car Corp. | added 7/55; 10/57-1/80 | | NRHS |
| 28 | MRRX | General Electric Railcar Services Corp. | 1/94; eliminated 10/94 | | NRHS |
| 29 | MRRX | *(NATX) GEN. ELECT. RAILCAR SERVICES CORP. [MATHER REFRIG. EXPRESS (NCCO); MATHER HORSE & STOCK CAR CO.] | | | PWRC |
| 30 | MRRX | *JOHN MORRELL & CO. (NCCO) | | | PWRC |
| 31 | MRRX | +MURPHY ROAD RECYCLING LLC | | | PWRC |
| 32 | MRRX | Murphy Road Recycling | | | RSRV |
| 33 | MRRX | MURPHY ROAD RECYCLING LLC | | | SCAC4 |
