Airlines — O
- OCNO Air
- OCMO'Connor Airlines
- OHKOasis Hong Kong Airlines
- IXOOCEAN AIR CARGO
- VCXOcean Airlines
- OCSOcean Sky (UK)
- TUKOcean Wings Commuter Service
- ONEOceanair
- ODSOdessa Airlines
- ODYOdyssey International
- FOCOffice Federal De'Aviation Civile
- GBOOgooue Air Cargo
- OKJOkada Airlines
- OKPOkapi Airways
- OKAOkay Airways
- OKLOklahoma Department of Public Safety
- OLXOlimex Aerotaxi
- KVKOlimp Air
- OALOlympic Airlines
- OLYOlympic Aviation
- OMAOman Air
- ORFOman Royal Flight
- OAVOmni - Aviacao e Tecnologia
- OAEOmni Air International
- OMFOmniflys
- OMSOmskavia Airline
- ORLOn Air Limited
- OTGOne Two Go Airlines
- 1CHOneChina
- OTMOnetime Airlines Zambia
- MEDOntario Ministry of Health
- OHYOnur Air
- OPAOpal Air
- OSYOpen Skies Consultative Commission
- OSAOpen Sky Aviation
- BOSOpenSkies
- OLEOperadora de Lineas Ejecutivas
- OTPOperadora de Transportes Aereos
- OPVOperadora de Veulos Ejectutivos
- ORROperadora Turistica Aurora
- LLOOperation Enduring Freedom
- OAXOperational Aviation Services
- ORDOrange Air Services
- ORJOrange Air Sierra Leone
- OREOrange Aviation
- OBSOrbest
- OBTOrbit Airlines
- OABOrbit Airlines Azerbaijan
- OANOrbit Atlantic Airways
- ORXOrbit Express Airlines
- OAIOrbit International Airlines
- OAROrbit Regional Airlines
- ORKOrca Air
- ORCOrchid Airlines
- BUEOrebro Aviation
- ORMOrel State Air Enterprise
- ORBOrenburg Airlines
- ORGOrenburzhie
- OTAOrganizacion De Transportes Aereos
- OMLOrganizacoes Mambra
- OVVOrient Air
- OTROrient Airlines
- ORNOrient Airways
- OEAOrient Thai Airlines
- NGKOriental Air Bridge
- OACOriental Airlines
- OGNOrigin Pacific Airways
- OEDOrion Air Charter
- OIXOrion-x
- KOVOrlan-2000
- RNGOrnage Aircraft Leasing
- OADOrscom Tourist Installations Company
- JPAOSACOM
- OSHOsh Avia
- OCOOstend Air College
- OLTOstfriesische Lufttransport
- FNLOulun Tilauslento
- RONOur Airline
- OOTOut Of The Blue Air Safaris
- OLAOverland Airways
- OXEOxaero
- WDKOxford Air Services
- OAAOxley Aviation
- OZROzark Air Lines
- OZJOzjet Airlines