| 1 | ONE | Oceanair Linhas Aereas Ltda | IATA: O6, Callsign: Oceanair, IATA Prefix: 247, Name changed to Oceanair Linhas Aereas Ltda t/a Avianca Brazil w.e.f. 26 March 2010. | BR | AVCODES |
| 2 | ONE | Oceanair Linhas Aereas Ltda t/a Avianca Brazil | IATA: O6, Callsign: Oceanair, IATA Prefix: 247, Ceased operations on 24 May 2019. Name changed from Oceanair Linhas Aereas Ltda w.e.f. 26 March 2010. | BR | AVCODES |
| 3 | ONE | Oceanair | IATA: O6 | | ICAO1 |
| 4 | ONE | one (London Eastern Railway Ltd,) | ‘one’ is the brand name of London Eastern Railway Ltd, which operates local, suburban and express services from London Liverpool Street in the City of London to East and North London, Essex, Hertfordshire, Cambridgeshire and East Anglia, otherwise known as the Greater Anglia network. ‘one’ is part of the National Express Group. The Greater Anglia network was awarded to a single operator as part of a drive to reduce the number of train companies operating to major termini, in an effort to improve integration between services and reliability. On April 1, 2004 ‘one’ took over all services formerly operated by Anglia Railways and First Great Eastern, as well as the ‘West Anglia’ services of WAGN. The company is now the sole passenger operator on most of the Great Eastern | GB | TRAFFIC |
| 5 | ONE | One (Greater Anglia Rail Franchise) | | UK | VKM |
| 6 | ONEA | ONEAL, CARL TRUCK LINE, INC | | | SCAC3 |
| 7 | ONEB | ORANGE NEWARK ELIZABETH BUS INC | | | SCAC3 |
| 8 | ONEB | ONE ONE SEVEN FIVE ZERO FOUR | | | SCAC4 |
| 9 | ONED | ONEIDA-COLUMBIA EXPRESS COMPANY | | | SCAC3 |
| 10 | ONED | ONE STOP KITCHEN IDEA LTD | | | SCAC4 |
| 11 | ONEE | ONEALES TRANSPORT INC | | | SCAC3 |
| 12 | ONEE | ONEALES TRANSPORT INC | | | SCAC4 |
| 13 | ONEF | ONE FIVE ONE FOUR | | | SCAC4 |
| 14 | ONEG | ONEGO SHIPPING AND CHARTERING B V | | | SCAC4 |
| 15 | ONEH | ONE HORN TRUCKING | | | SCAC4 |
| 16 | ONEI | OVERNIGHT NEW ENGLAND INC | | | SCAC3 |
| 17 | ONEJ | ONEAL, CLAUDE C JR | | | SCAC3 |
| 18 | ONEJ | ONE A (1A) ENTERPRISES | | | SCAC4 |
| 19 | ONEL | ONEL TRANSPORTATION INC | | | SCAC4 |
| 20 | ONEN | ONTARIO-NEW ENGLAND EXPRESS INC | | | SCAC4 |
| 21 | ONEP | ONE (#1) PRIORITY TRANSPORT | | | SCAC3 |
| 22 | ONEQ | O N E SHIPPING INC. | | | SCAC3 |
| 23 | ONEQ | ONE SEVEN EIGHT FOUR FOUR TWO FOUR | | | SCAC4 |
| 24 | ONER | Ontario Eastern R.R. Corp. | added 7/1982; eliminated 4/1986 | | NAKINA |
| 25 | ONER | Ontario Eastern R.R. Corp. | added 7/82; eliminated 4/86 | | NRHS |
| 26 | ONER | ONTARIO EASTERN RAILROAD | | | PWRC |
| 27 | ONER | Ontario Eastern Railroad | | | RSRV |
| 28 | ONER | OHIO NORTHERN EXPRESS INC | | | SCAC4 |
| 29 | ONES | O N E SHIPPING LTD | | | SCAC3 |
| 30 | ONES | ONE FIVE NINE EIGHT SIX SIX FIVE (1 | | | SCAC4 |
| 31 | ONET | ONEAL TRUCKING | | | SCAC3 |
| 32 | ONEU | OCEAN NETWORK EXPRESS PTE. LTD. | | SGP | BIC |
| 33 | ONEU | ONE WAY LEASE INC | | | SCAC4 |
| 34 | ONEW | ONE WORLD LOGISTICS OF AMERICA INC | | | SCAC4 |
| 35 | ONEX | Oneta Refining Co. | 8/1920-7/1923 | | NAKINA |
| 36 | ONEX | ONETA REFINING CO. | | | PWRC |
| 37 | ONEY | ORATEL NETWORKS | | | SCAC4 |
