| HNL | PHNL | Oahu see Honolulu International Airport, United States |
| OAK | KOAK | Oakland International Airport, United States |
| OAX | MMOX | Oaxaca Airport, Mexico |
| OBO | RJCB | Obihiro - Tokachi Obihiro Airport, Japan |
| SBY | KSBY | Ocean City see Salisbury/Ocean City Regional Airport, United States |
| LEH | LFOH | Octeville Airport see Le Havre/Octeville Aeroport, France |
| ODE | EKOD | Odense Airport, Denmark |
| ODS | UKOO | Odessa Airport, Ukraine |
| ORD | KCHI | O´Hare Airport see Chicago - O´Hare Airport, United States |
| OHD | LWOH | Ohrid Airport, Macedonia |
| OIT | RJFO | Oita Airport, Japan |
| OKJ | RJOB | Okayama Airport, Japan |
| WAW | EPWA | Okecie Airport see Warsaw - Frederic Chopin Airport, Poland |
| OKC | KOKC | Oklahoma City-Will Rogers World Airport, United States |
| OLB | LIEO | Olbia-Costa Smerelda Airport, Italy |
| OMA | KOMA | Omaha-Eppley Airfield, United States |
| RHI | KRHI | Oneida County Airport see Rhinelander - Oneida County Airport, United States |
| ONT | KONT | Ontario Int´l Airport, United States |
| OPO | LPPR | Oporto - Francisco Sá Carneiro Airport, Portugal |
| SNA | KSNA | Orange County see Santa Ana - John Wayne Airport, United States |
| ORB | ESOE | Örebro Airport, Sweden |
| BGY | LIME | Orio Al Serio Airport see Milan - Orio Al Serio Airport, Italy |
| EOI | EGED | Orkney Is - Eday Airstrip, United Kingdom |
| KOI | EGPA | Orkney Is.-Kirkwall Airport see Kirkwall Airport, United Kingdom |
| NRL | EGEN | Orkney Is - N Ronaldsay Airstrip, United Kingdom |
| MCO | KMCO | Orlando International Airport, United States |
| SFB | KSFB | Orlando Sanford International Airport, United States |
| ORY | LFPO | Orly Airport see Paris - Orly Airport, France |
| OER | ESNO | Örnsköldsvik Airport, Sweden |
| ITM | RJOO | Osaka - Itami International Airport, Japan |
| KIX | RJBB | Osaka - Kansai International Airport, Japan |
| OSI | LDOS | Osijek Airport, Croatia |
| GEN | ENGM | Oslo - Gardermoen Airport, Norway |
| ZOS | SCJO | Osorno Aerodrome - Cañal Bajo, Chile |
| LDE | LFBT | Ossun Airport see Tarbes-Lourdes-Pyrenées Airport, France |
| OST | EBOS | Ostend-Bruges International Airport, Belgium |
| OSD | ESPC | Östersund Airport, Sweden |
| OSR | LKMT | Ostrava Int´l Airport, Czech Republic |
| BXO | GGOV | Osvaldo Vieira Airport see Bissau - Osvaldo Vieira Airport, Guinea Bissau |
| OTP | LROP | Otopeni Airport see Bucharest - Henri Coanda International Airport, Romania |
| YOW | CYOW | Ottawa Int´l Airport, Canada |
| OUA | DFFD | Ouagadougou Airport, Burkina Faso |
| OGX | DAUU | Ouargla Airport, Algeria |
| OZZ | GMMZ | Ouarzazate Airport, Morocco |
| OUD | GMFO | Oujda Angads Airport, Morocco |
| OUL | EFOU | Oulu Airport, Finland |
| ATW | KATW | Outagamie County Airport see Appleton/Outagamie County Regional Airport, United States |
| GCM | MWCR | Owen Roberts Airport see Grand Cayman-Owen Roberts Int´l Airport, Carib,Cayman Islands |
| OXF | EGTK | Oxford Airport, United Kingdom |
