| OAK | Oakland International Airport |
| OAX | Oaxaca Airport |
| ODB | Cordoba Airport |
| ODE | Odense Airport |
| ODS | Odessa Airport |
| OER | Örnsköldsvik Airport |
| OGG | Kahului Airport |
| OHD | Ohrid Airport |
| OKA | Okinawa/Naha Airport |
| OKC | Oklahoma City-Will Rogers World Airport |
| OKJ | Okayama Airport |
| OLB | Olbia-Costa Smerelda Airport |
| OMA | Omaha-Eppley Airfield |
| OMO | Mostar Airport |
| ONT | Ontario Int´l Airport |
| OOL | Coolangatta Airport - Gold Coast Airport |
| OPO | Oporto - Francisco SA Carneiro Airport |
| ORB | Örebro Airport |
| ORD | Chicago - O´Hare Airport |
| ORF | Norfolk International Airport |
| ORH | Worcester Regional Airport |
| ORY | Paris - Orly Airport |
| OSD | Östersund Airport |
| OSI | Osijek Airport |
| OSR | Letiste Ostrava as |
| OSR | Ostrava Int´l Airport |
| OST | Ostend/Bruges International Airport |
| OTP | Bucharest - Henri Coanda International Airport |
| OUA | Ouagadougou Airport |
| OUD | Oujda Angads Airport |
| OUL | Oulu Airport |
| OVB | Novosibirsk Tolmachevo Airport |
| OVD | Asturias Airport |
| OXF | Oxford Airport |
| OZZ | Ouarzazate Airport |
