| 1 | NIR | Norsk Flytjeneste AS | Callsign: Norseman, Founded in 1961. Merged into Wideroe in 1996. ICAO designator changed from PEN | N | AVCODES |
| 2 | NIR | Norsk Flyrjeneste | | | ICAO1 |
| 3 | NIR | NORTHEAST ILLINOIS RAILROAD CORP. | | | PWRC |
| 4 | NIR | Northern Ireland Railways Company Limited | | GB | TRAFFIC |
| 5 | NIR | Northern Ireland Railways Company Limited | | UK | VKM |
| 6 | NIRA | NIAGARA LOGISTICS INC | | | SCAC4 |
| 7 | NIRC | NORTHEAST ILLINOIS REGIONAL COMMUTER RAILROAD CORP. (METRA) | | | PWRC |
| 8 | NIRH | NICHOLS, ROBERT HAULING | | | SCAC3 |
| 9 | NIRH | NICHOLS, ROBERT TRUCKING INC | | | SCAC4 |
| 10 | NIRI | NIRINT SHIPPING BV | | | SCAC4 |
| 11 | NIRO | NiRoVe GmbH | | DE | VKM |
| 12 | NIRS | NICHOLSON AIR SERVICES | | | SCAC3 |
| 13 | NIRU | NIRINT SHIPPING BV | | NL | BIC |
| 14 | NIRU | NIRINT SHIPPING BV | | | SCAC4 |
| 15 | NIRV | NIRVANA TRANSPORT INC | | | SCAC4 |
| 16 | NIRX | General Electric Rail Services Corp. | added 1/2000; 7/2000-7/2005 | | NAKINA |
| 17 | NIRX | General Electric Railcar Services Corp. | added 1/1984; 1/1994; eliminated 1/2000 | | NAKINA |
| 18 | NIRX | North American Car Corp. | added 4/1962; 7/1965-1/1980; eliminated 1/1984 | | NAKINA |
| 19 | NIRX | North American Car Corp. | added 4/62; 7/65-1/80 | | NRHS |
| 20 | NIRX | General Electric Railcar Services Corp. | 1/94; eliminated 1/2000 | | NRHS |
| 21 | NIRX | General Electric Rail Services Corp. | added 1/2000; 7/2000 | | NRHS |
| 22 | NIRX | (NATX) GENERAL ELECTRIC RAIL SERVICES CORP. [NORTH AMERICAN CAR CORP.] | | | PWRC |
| 23 | NIRX | GE Rail Services | | | RSRV |
| 24 | NIRX | GENERAL ELECTRIC RAILCAR SERVICES C | | | SCAC4 |
