| 1 | NCO | Natalco Air Lines | Callsign: Natalco, | STP | AVCODES |
| 2 | NCO | NAVCO (Airways) Ltd. | Callsign: NAVCO, | GB | AVCODES |
| 3 | NCO | Natalco Air Lines | | | ICAO1 |
| 4 | NCOA | NORTH COAST OUTFITTERS LTD | | | SCAC4 |
| 5 | NCOC | NORCO CORPORATION | | | SCAC4 |
| 6 | NCOE | NOW COURIER INC | | | SCAC3 |
| 7 | NCOH | NATIONAL CARRIERS OF AMERICA INC | | | SCAC4 |
| 8 | NCOK | North Central Oklahoma Ry., Inc. | added 4/1982; eliminated 4/1985 | | NAKINA |
| 9 | NCOK | North Central Oklahoma Ry., Inc. | added 4/82; eliminated 4/85 | | NRHS |
| 10 | NCOK | NORTH CENTRAL OKLAHOMA RAILWAY | | | PWRC |
| 11 | NCOK | North Central Oklahoma Railway | | | RSRV |
| 12 | NCOM | NORTHERN COLORADO MOVING & STORAGE | | | SCAC3 |
| 13 | NCOP | NATIONAL COMPRESSOR EXCHANGE | | | SCAC3 |
| 14 | NCOR | NALC CORP | | | SCAC4 |
| 15 | NCOS | NICHOLS TRUCKING COMPANY | | | SCAC3 |
| 16 | NCOS | NELS CONSULTING SERVICES INC | | | SCAC4 |
| 17 | NCOST | Nuove Costruzioni S.r.l. | | IT | VKM |
| 18 | NCOT | NOEL CORPORATION | | | SCAC4 |
| 19 | NCOU | ARTEL STARATELEY SHUKOTKA LTD | | | SCAC4 |
| 20 | NCOX | Newport Division, Tenneco Chemicals, Inc. | added 7/1965; 7/1965; eliminated 10/1966 | | NAKINA |
| 21 | NCOX | Newport Division, Heyden Newport Chemical Corp. | eliminated 7/1965 | | NAKINA |
| 22 | NCOX | Newport Industries Division, Heyden Newport Chemical Corp. | added 4/1961; 4/1961 | | NAKINA |
| 23 | NCOX | Newport Industries Co., a Division of Heyden Newport Chemical Corp. | added 4/1957; 10/1957; eliminated 4/1961 | | NAKINA |
| 24 | NCOX | Newport Industries, Inc. | 7/1937-7/1954; eliminated 4/1957 | | NAKINA |
| 25 | NCOX | The Newport Co. (Newport Industries, Inc.) | 7/1932-7/1935 | | NAKINA |
| 26 | NCOX | The Newport Co. | 7/1930 | | NAKINA |
| 27 | NCOX | Newport Industries, Inc. | 4/38-1/52; eliminated 4/57 | | NRHS |
| 28 | NCOX | Newport Industries Co., a Division of Heyden Newport Chemical Corp. | added 4/57; 10/57; eliminated 4/61 | | NRHS |
| 29 | NCOX | Newport Industries Division, Heyden Newport Chemical Corp. | added 4/61; 4/61 | | NRHS |
| 30 | NCOX | Newport Division, Heyden Newport Chemical Corp. | eliminated 7/65 | | NRHS |
| 31 | NCOX | Newport Division, Tenneco Chemicals, Inc. | added 7/65; 7/65; eliminated 10/66 | | NRHS |
| 32 | NCOX | *NEWPORT DICISION, TENNECO CHEMICALS, INC. | | | PWRC |
| 33 | NCOX | *NORTH CENTRAL OKLAHOMA & MIDLANDS RAILWAY | | | PWRC |
| 34 | NCOX | NEWPORT DIV TENNECO CHEMICALS INC | | | SCAC3 |