| OAK | KOAK | Oakland International Airport, United States |
| OAX | MMOX | Oaxaca Airport, Mexico |
| OBO | RJCB | Obihiro - Tokachi Obihiro Airport, Japan |
| ODB | LEBA | Cordoba Airport, Spain |
| ODE | EKOD | Odense Airport, Denmark |
| ODS | UKOO | Odessa Airport, Ukraine |
| OER | ESNO | Örnsköldsvik Airport, Sweden |
| OGG | PHOG | Kahului Airport, United States |
| OGX | DAUU | Ouargla Airport, Algeria |
| OHD | LWOH | Ohrid Airport, Macedonia |
| OIT | RJFO | Oita Airport, Japan |
| OKA | ROAH | Naha Airport, Japan |
| OKC | KOKC | Oklahoma City-Will Rogers World Airport, United States |
| OKJ | RJOB | Okayama Airport, Japan |
| OLB | LIEO | Olbia-Costa Smerelda Airport, Italy |
| OMA | KOMA | Omaha-Eppley Airfield, United States |
| OMO | LQMO | Mostar Airport OMO/LQMO, Bosnia-Herzegovina |
| ONT | KONT | Ontario Int´l Airport, United States |
| OOL | YBCG | Coolangatta - Gold Coast Airport, Australia |
| OPO | LPPR | Oporto - Francisco Sá Carneiro Airport, Portugal |
| ORB | ESOE | Örebro Airport, Sweden |
| ORD | KCHI | Chicago - O´Hare Airport, United States |
| ORF | KORF | Norfolk International Airport, United States |
| ORH | KORH | Worcester Regional Airport, United States |
| ORY | LFPO | Paris - Orly Airport, France |
| OSB | ORBM | Mosul International Airport, Iraq |
| OSD | ESPC | Östersund Airport, Sweden |
| OSI | LDOS | Osijek Airport, Croatia |
| OSR | LKMT | Letiste Ostrava as, Czech Republic |
| OSR | LKMT | Ostrava Int´l Airport, Czech Republic |
| OST | EBOS | Ostend-Bruges International Airport, Belgium |
| OTP | LROP | Bucharest - Henri Coanda International Airport, Romania |
| OUA | DFFD | Ouagadougou Airport, Burkina Faso |
| OUD | GMFO | Oujda Angads Airport, Morocco |
| OUL | EFOU | Oulu Airport, Finland |
| OVB | UNNT | Novosibirsk Tolmachevo Airport, Russia |
| OVD | LEAS | Asturias Airport, Spain |
| OXF | EGTK | Oxford Airport, United Kingdom |
| OZH | UKDE | Zaporizhzya International Airport, Ukraine |
| OZZ | GMMZ | Ouarzazate Airport, Morocco |
