| 1 | C&A | Alton R.R. | 4/1938-7/1954 | | NAKINA |
| 2 | C&A | The Chicago and Alton R.R. Co. (The Alton R.R. Co.) | 7/1932-7/1936 | | NAKINA |
| 3 | C&A | The Chicago and Alton R.R. Co. | 8/1920-7/1930 | | NAKINA |
| 4 | C&A | The Chicago and Alton R.R. Co. | 23-Jul | | NRHS |
| 5 | C&A | Alton R.R. | 4/38-1/52 | | NRHS |
| 6 | C&A | CHICAGO & ALTON RR OR ALTON RR | | | PWRC |
| 7 | C&C | Coal & Coke Ry. | 8/1920 | | NAKINA |
| 8 | C&C | *CARTHAGE & COPENHAGEN RAILROAD | | | PWRC |
| 9 | C&C | *COAL & COKE RWY. | | | PWRC |
| 10 | C&C | *COLUMBIA & COWLITZ RAILWAY COMPANY | | | PWRC |
| 11 | C&CA | Canton & Carthage R.R. | 4/1938-4/1961 | | NAKINA |
| 12 | C&CA | Canton & Carthage R.R. | 4/38-4/61 | | NRHS |
| 13 | C&CA | CANTON & CARTHAGE RAILROAD | | | PWRC |
| 14 | C&EI | Chicago & Eastern Illinois R.R. | 10/1957-10/1966 | | NAKINA |
| 15 | C&EI | Chicago & Eastern Illinois Ry. Co. | 8/1920-/1954 | | NAKINA |
| 16 | C&EI | Chicago & Eastern Illinois Ry. Co. | 23-Jul | | NRHS |
| 17 | C&EI | Chicago & Eastern Illinois R.R. | 4/38-10/66 | | NRHS |
| 18 | C&EI | UP [MISSOURI PACIFIC] [CHICAGO & EASTERN ILLINOIS RY] | | | PWRC |
| 19 | C&G | Columbus & Greenville Ry. Co. | 7/1930-10/1966 | | NAKINA |
| 20 | C&G | Columbus & Greenville R.R. Co. | 7/1923 | | NAKINA |
| 21 | C&G | Columbus & Greenville R.R. Co. | 23-Jul | | NRHS |
| 22 | C&G | Columbus & Greenville Ry. Co. | 4/38-10/66 | | NRHS |
| 23 | C&G | COLUMBUS & GREENVILLE RY | | | PWRC |
| 24 | C&I | CAMBRIA & INDIANA RAILROAD COMPANY | | | PWRC |
| 25 | C&IC | Cedar Rapids and Iowa City Ry. | 7/1923-7/1936 | | NAKINA |
| 26 | C&IC | Cedar Rapids and Iowa City Ry. | 23-Jul | | NRHS |
| 27 | C&IC | CEDAR RAPIDS & IOWA CITY RWY. | | | PWRC |
| 28 | C&IM | Chicago & Illinois Midland Ry. | 4/1938-1/1952 | | NAKINA |
| 29 | C&IM | Chicago & Illinois Midland Ry. Co. | 8/1920-7/1936 | | NAKINA |
| 30 | C&IM | Chicago & Illinois Midland Ry. Co. | 23-Jul | | NRHS |
| 31 | C&IM | Chicago & Illinois Midland Ry. | 4/38-1/52 | | NRHS |
| 32 | C&IM | CHICAGO & MIDLAND RWY. CO. (OUT OF EXISTENCE) | | | PWRC |
| 33 | C&IW | Chicago & Illinois Western R.R. | 7/1935-1/1952 | | NAKINA |
| 34 | C&IW | Chicago & Illinois Western R.R. | 4/38-1/52 | | NRHS |
| 35 | C&IW | CHICAGO & ILLINOIS WESTERN RAILROAD | | | PWRC |
| 36 | C&L | Cornwall & Lebanon R.R. (Penna. R.R.) | 7/1930 | | NAKINA |
| 37 | C&L | Cornwall & Lebanon R.R. (Penna. R.R. System) | 8/1920-7/1923 | | NAKINA |
| 38 | C&L | Cornwall & Lebanon R.R. (Penna. R.R. System) | 23-Jul | | NRHS |
| 39 | C&L | PENNSYLVANIA RAILROAD [CORNWALL & LEBANON RAILROAD] | | | PWRC |
| 40 | C&LS | CHICAGO & LAKE SUPERIOR RWY | | | PWRC |
| 41 | C&M | Cumberland & Manchester R.R. Co. (Louisville & Nashville R.R. Co.) | 7/1930-7/1936 | | NAKINA |
| 42 | C&M | LOUISVILLE & NASHVILLE rAILROAD [CUMBERLAND & MANCHESTER RAILROAD CO.] | | | PWRC |
| 43 | C&NW | UP [CHICAGO & NORTH WESTERN TRANS CO] [CHICAGO & NORTH WESTERN RWY.] | | | PWRC |
| 44 | C&O | Chesapeake & Ohio Ry. | 4/1938-10/1966 | | NAKINA |
| 45 | C&O | Chesapeake & Ohio Ry. Co. | 7/1930-7/1936 | | NAKINA |
| 46 | C&O | C. & O. Lines (C. & O. Ry.) | 7/1923 | | NAKINA |
| 47 | C&O | C. & O. Lines (C. & O. Ry.) | 23-Jul | | NRHS |
| 48 | C&O | Chesapeake & Ohio Ry. | 4/38-10/66 | | NRHS |
| 49 | C&O | CSX TRANSPORTATION, INC. [CHESAPEAKE & OHIO RY] | | | PWRC |
| 50 | C&PA | Cumberland & Pennsylvania R.R. Co. | 8/1920-7/1936 | | NAKINA |
| 51 | C&PA | Cumberland & Pennsylvania R.R. Co. | 23-Jul | | NRHS |
| 52 | C&PA | CUMBERLAND & PENNSYLVANIA RAILROAD CO. | | | PWRC |
| 53 | C&S | Colorado & Southern Ry. | 4/1938-10/1966 | | NAKINA |
| 54 | C&S | Colorado & Southern Ry. Co. | 8/1920-7/1936 | | NAKINA |
| 55 | C&S | Colorado & Southern Ry. Co. | 23-Jul | | NRHS |
| 56 | C&S | Colorado & Southern Ry. | 4/38-10/66 | | NRHS |
| 57 | C&S | BNSF [BURLINGTON NORTHERN RAILROAD CO; COLORADO & SOUTHERN] | | | PWRC |
| 58 | C&SE | Colorado & Southeastern R.R. | 4/1938-7/1954 | | NAKINA |
| 59 | C&SE | Colorado & South-Eastern R.R. Co. | 7/1930-7/1936 | | NAKINA |
| 60 | C&SE | Colorado & Southeastern R.R. Co. | 7/1923 | | NAKINA |
| 61 | C&SE | Colorado & Southeastern R.R. Co. | 23-Jul | | NRHS |
| 62 | C&SE | Colorado & Southeastern R.R. | 4/38-1/52 | | NRHS |
| 63 | C&SE | COLORADO & SOUTHEASTERN RAILROAD CO. | | | PWRC |
| 64 | C&T | CATSKILL & TANNERSVILLE RAILROAD | | | PWRC |
| 65 | C&WC | Charleston & Western Carolina Ry. Co. (Atlantic Coast Line R.R. Co.) | 10/1966 | | NAKINA |
| 66 | C&WC | Charleston & Western Carolina R.R. | 4/1938-7/1965 | | NAKINA |
| 67 | C&WC | Charleston & Western Carolina Ry. Co. | 8/1920-7/1936 | | NAKINA |
| 68 | C&WC | Charleston & Western Carolina Ry. Co. | 23-Jul | | NRHS |
| 69 | C&WC | Charleston & Western Carolina R.R. | 4/38-7/65 | | NRHS |
| 70 | C&WC | Charleston & Western Carolina Ry. Co. (Atlantic Coast Line R.R. Co.) | Oct-66 | | NRHS |
| 71 | C&WC | ATLANTIC COAST LINE RAILROAD CO.[CHARLESTON & WESTERN CAROLINA RWY. CO.] | | | PWRC |
| 72 | C&WI | Chicago & Western Indiana R.R. Co. | 8/1920-7/1936 | | NAKINA |
| 73 | C&WI | Chicago & Western Indiana R.R. Co. | 23-Jul | | NRHS |
| 74 | C&WI | CHICAGO & WESTERN INDIANA RAILROAD CO. | | | PWRC |
| 75 | C0 | Nowy Przewoznik | ICAO: CLW, Callsign: Centralwings, Founded in 2004. Ceased operations on 26 March 2009. Designator C0* recalled by IATA | PL | AVCODES |
| 76 | C0 | One Caribbean Ltd. | ICAO: VCY, Callsign: Vincy, | WV | AVCODES |
| 77 | C1 | Techtimes Sudamericana S.A. | Computer Reservations Systems (CRS) | RA | AVCODES |
| 78 | C2 | Mountain Air Cargo, Inc. | ICAO: MTN, Callsign: Mountain, Designator C2* recalled by IATA. | USA | AVCODES |
| 79 | C2 | Air Caribbean Limited | ICAO: CBB, Callsign: Ibis, | TT | AVCODES |
| 80 | C2 | Air Luxor STP | ICAO: ALU, Callsign: Luxorjet, | STP | AVCODES |
| 81 | C2 | Ceiba Intercontinental | ICAO: CEL, Callsign: Ceiba Line, IATA Prefix: 304, | GQ | AVCODES |
| 82 | C2C | c2c Rail (former LTS Rail Ltd.) | 1999: 128km standard gauge, electrified at 25kV 50Hz c2c is a train operating company that provides train services, on a franchise basis, on the London, Tilbury & Southend line from Fenchurch Street in the City of London to East London and the entire length of the northern Thames Gateway area including Basildon, Chafford Hundred (for Lakeside), Tilbury and Southend. | GB | TRAFFIC |
| 83 | C3 | Independent Carrier (ICAR) | ICAO: IPR, Callsign: Air Icar, IATA Prefix: 655, IATA designator changed from C3* | UA | AVCODES |
| 84 | C3 | Independent Carrier (ICAR) | ICAO: IPR, Callsign: Air Icar, IATA Prefix: 655, IATA designator reinstated | UA | AVCODES |
| 85 | C3 | Contactair GmbH & Co. | ICAO: KIS, Callsign: Contactair, Merged with OLT Express Germany on 01 September 2012. Designator C3 reinstated by IATA. Name changed from Contactair Flugdienst and Co. | D | AVCODES |
| 86 | C3 | Independent Carrier (ICAR) | ICAO: IPR, IATA designator changed to C3 | UA | AVCODES |
| 87 | C3 | Sky Capital Airlines Ltd | ICAO: AHW, IATA Prefix: 400, Founded in 2009. | BD | AVCODES |
| 88 | C3 | Trade Air d.o.o. | ICAO: TDR, Callsign: Tradeair, IATA designator changed from 8P* | HR | AVCODES |
| 89 | C3 | Cargo Three, Inc. (Cargo Tres, Sociedad Anónima) | ICAO: CTW, Callsign: Third Cargo, IATA Prefix: 364, | PA | AVCODES |
| 90 | C4 | Zimex Aviation Limited | ICAO: IMX, Callsign: Zimex, IATA designator changed from MF | CH | AVCODES |
| 91 | C4 | Airlines of Carriacou Limited | ICAO: COU, Designator C4 recalled by IATA | WG | AVCODES |
| 92 | C4 | Aerolineas Mesoamericanas, S.A. de C.V. d/b/a ALMA de Mexico | ICAO: MSO, Callsign: Alma, IATA Prefix: 665, Founded in 2005. Commenced operations on 12 June 2006. Ceased operations on 07 November 2008. | MEX | AVCODES |
| 93 | C4 | Conquest Air, Inc. | ICAO: QAI, Callsign: Chickpea, IATA Prefix: 340, | USA | AVCODES |
| 94 | C5 | Champlain Enterprises, LLC. t/a CommutAir | ICAO: UCA, Callsign: Commutair, IATA Prefix: 841, Name changed from Commutair (US Airways Express) | USA | AVCODES |
| 95 | C5 | Cretan Airlines | ICAO: KRT, Callsign: Cretan, Ceased operations | GR | AVCODES |
| 96 | C5 | Ukraine Airservice Airlines | ICAO: ASG, IATA designator changed to 9G* | UA | AVCODES |
| 97 | C5 | Asociados Latinamericanos de Transport Aereo S.A. (A.L.T.A.) | | RCH | AVCODES |
| 98 | C6 | CanJet Airlines | ICAO: CJA, Callsign: Canjet, Founded in 1999 and commenced operations on 05 September 2000. Wholly owned by IMP Group International. Merged into Canada 3000 24 April 2001. | CDN | AVCODES |
| 99 | C6 | Unilode Aviation Solutions New Zealand Limited | Non-airline Unit Load Devices (ULD) companies | NZ | AVCODES |
| 100 | C6 | CanJet Airlines | ICAO: CJA, Callsign: Canjet, Relaunched on 20 June 2002. Suspeneded all operations on 01 September 2015. Wholly owned by IMP Group International. | CDN | AVCODES |
