| ICAO | IATA | NAME |
|---|
| OCN | | O Air |
| CR | OAG |
| OHK | O8 | Oasis Hong Kong Airlines |
| BCN | | Ocean Air |
| VCX | VC | Ocean Airlines |
| OCS | | Ocean Sky (UK) |
| TUK | | Ocean Wings Commuter Service |
| ONE | O6 | Oceanair |
| O2 | Oceanic Airlines |
| ODS | | Odessa Airlines |
| ODY | | Odyssey International |
| GBO | | Ogooue Air Cargo |
| OKJ | | Okada Airlines |
| OKP | | Okapi Airways |
| OKA | | Okay Airways |
| OKL | | Oklahoma Department of Public Safety |
| OLX | | Olimex Aerotaxi |
| KVK | | Olimp Air |
| OAL | OA | Olympic Airlines |
| OLY | | Olympic Aviation |
| OMA | WY | Oman Air |
| ORF | | Oman Royal Flight |
| OAV | | Omni - Aviacao e Tecnologia |
| OAE | OY | Omni Air International |
| OMF | | Omniflys |
| OMS | N3 | Omskavia Airline |
| ORL | | On Air Limited |
| OTG | | One Two Go Airlines |
| OTM | | Onetime Airlines Zambia |
| TRI | | Ontario Government |
| MED | | Ontario Ministry of Health |
| OHY | 8Q | Onur Air |
| OPA | | Opal Air |
| OSY | 1L | Open Skies Consultative Commission |
| OSA | | Open Sky Aviation |
| BOS | | OpenSkies |
| OLE | | Operadora de Lineas Ejecutivas |
| OTP | | Operadora de Transportes Aereos |
| OPV | | Operadora de Veulos Ejectutivos |
| ORR | | Operadora Turistica Aurora |
| LLO | | Operation Enduring Freedom |
| OAX | | Operational Aviation Services |
| ORD | | Orange Air Services |
| ORJ | | Orange Air Sierra Leone |
| ORE | | Orange Aviation |
| ORX | | Orbit Express Airlines |
| ORK | | Orca Air |
| BUE | | Orebro Aviation |
| ORM | | Orel State Air Enterprise |
| ORB | R2 | Orenburg Airlines |
| OTA | | Organizacion De Transportes Aereos |
| OML | | Organizacoes Mambra |
| OVV | | Orient Air |
| OTR | | Orient Airlines |
| ORN | | Orient Airways |
| OEA | OX | Orient Thai Airlines |
| NGK | | Oriental Air Bridge |
| OAC | | Oriental Airlines |
| OGN | QO | Origin Pacific Airways |
| OED | | Orion Air Charter |
| OIX | | Orion-x |
| KOV | | Orlan-2000 |
| RNG | | Ornage Aircraft Leasing |
| OAD | | Orscom Tourist Installations Company |
| JPA | | OSACOM |
| OSH | | Osh Avia |
| OCO | | Ostend Air College |
| OLT | OL | Ostfriesische Lufttransport |
| FNL | | Oulun Tilauslento |
| RON | ON | Our Airline |
| OOT | | Out Of The Blue Air Safaris |
| OLA | OJ | Overland Airways |
| OXE | | Oxaero |
| WDK | | Oxford Air Services |
| OAA | | Oxley Aviation |
| OZR | OZ | Ozark Air Lines |
| OZJ | O7 | Ozjet Airlines |
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