| Oak Harbor | United States | ODW | More info |
| Oakey | Australia | OKY | More info |
| Oakland/Coliseum Stat | United States | OBT | More info |
| Oamaru | New Zealand (Aotearoa) | OAM | More info |
| Oban | Australia | OBA | More info |
| Oban Airport | United Kingdom | OBN | More info |
| Obano | Indonesia | OBD | More info |
| Obbia | Somalia | CMO | More info |
| Oberpfaffenhofen | Germany | OBF | More info |
| Obidos | Brazil | OBI | More info |
| Obihiro | Japan | OBO | More info |
| Obo | Papua New Guinea | OBX | More info |
| Obock | Djibouti | OBC | More info |
| Obre Lake | Canada | YDW | More info |
| Ocean Falls | Canada | ZOF | More info |
| Ocean Reef | United States | OCA | More info |
| Oceanic | United States | OCI | More info |
| Oconee County | United States | CEU | More info |
| Octeville | France | LEH | More info |
| Ocussi | Indonesia | OEC | More info |
| Odate Noshiro | Japan | ONJ | More info |
| Oddor Meanche | Cambodia | OMY | More info |
| Odessa Regional | United States | MAF | More info |
| Odienne | Cote D'Ivoire (Ivory Coast) | KEO | More info |
| Oenpelli | Australia | OPI | More info |
| Off Line Point | Hong Kong | ZJK | More info |
| Off line Point | Australia | XZX | More info |
| Off Line Point | Australia | WGZ | More info |
| Off Line Point | United Kingdom | WUK | More info |
| Off Line Point | Bahrain | WGF | More info |
| Off line Point | Germany | XZE | More info |
| Off line Point | United States | XZU | More info |
| Off line Point | Japan | XZJ | More info |
| Ofu | American Samoa | OFU | More info |
| Ogdensburg | United States | OGS | More info |
| Ogeranang | Papua New Guinea | OGE | More info |
| Ogle | Guyana | OGL | More info |
| Ogoki | Canada | YOG | More info |
| O'Hare International | United States | ORD | More info |
| Ohio County | United States | HLG | More info |
| Ohio State University | United States | OSU | More info |
| Ohio University | United States | ATO | More info |
| Ohrid | Yugoslavia | OHD | More info |
| Oiapoque | Brazil | OYK | More info |
| Oita | Japan | OIT | More info |
| Okaba | Indonesia | OKQ | More info |
| Okadama | Japan | OKD | More info |
| Okao | Papua New Guinea | OKV | More info |
| Okaukuejo | Namibia | OKF | More info |
| Okayama | Japan | OKJ | More info |
| Okhotsk | Russian Federation | OHO | More info |
| Oki Island | Japan | OKI | More info |
| Okino Erabu | Japan | OKE | More info |
| Okmulgee | United States | OKM | More info |
| Okondja | Gabon | OKN | More info |
| Okoyo | Congo | OKG | More info |
| Oksapmin | Papua New Guinea | OKP | More info |
| Oksibil | Indonesia | OKL | More info |
| Oktiabrskij | Russian Federation | OKT | More info |
| Okushiri | Japan | OIR | More info |
| Olafsfjordur | Iceland | OFJ | More info |
| Olanchito | Honduras | OAN | More info |
| Olavarria | Argentina | OVR | More info |
| Old Crow | Canada | YOC | More info |
| Old Fort Bay | Canada | ZFB | More info |
| Old Harbor SPB | United States | OLH | More info |
| Old Town | United States | OLD | More info |
| Olf Usn | United States | NEN | More info |
| Olga Bay SPB | United States | KOY | More info |
| Olive Branch Arpt | United States | OLV | More info |
| Olney | United States | ONY | More info |
| Olney-Noble | United States | OLY | More info |
| Olomouc | Czech Republic | OLO | More info |
| Olpoi | Vanuatu | OLJ | More info |
| Olsobip | Papua New Guinea | OLQ | More info |
| Olympia | United States | OLM | More info |
| Olympic Dam | Australia | OLP | More info |
| Omboue | Gabon | OMB | More info |
| Omega | Namibia | OMG | More info |
| Omidieh | Iran | OMI | More info |
| Omkalai | Papua New Guinea | OML | More info |
| Omora | Papua New Guinea | OSE | More info |
| Omsk | Russian Federation | OMS | More info |
| Omura | Japan | OMJ | More info |
| Ondangwa | Namibia | OND | More info |
| Oneal | United States | OEA | More info |
| Oneida County | United States | RHI | More info |
| Oneida County | United States | UCA | More info |
| Onepusu | Solomon Islands | ONE | More info |
| Ongava Game Reserve | Namibia | OGV | More info |
| Ongiva | Angola | VPE | More info |
| Onion Bay | United States | ONN | More info |
| Ono I Lau | Fiji | ONU | More info |
| Ononge | Papua New Guinea | ONB | More info |
| Onotoa | Kiribati | OOT | More info |
| Onslow | Australia | ONS | More info |
| Ontario International | United States | ONT | More info |
| Ontario Municipal Airport | United States | ONO | More info |
| Ontong Java | Solomon Islands | OTV | More info |
| Oodnadatta | Australia | ODD | More info |
| Opa Locka | United States | OPF | More info |
| Open Bay | Papua New Guinea | OPB | More info |
| Ophira International | Egypt | SSH | More info |
| Opuwa | Namibia | OPW | More info |
| Oradea | Romania | OMR | More info |
| Oram | Papua New Guinea | RAX | More info |
| Oran | Argentina | ORA | More info |
| Orange County | United States | MGJ | More info |
| Orange County Steel Salvage Heliport | United States | ANA | More info |
| Orange Walk | Belize | ORZ | More info |
| Oranjemund | Namibia | OMD | More info |
| Orapa | Botswana | ORP | More info |
| Orbost | Australia | RBS | More info |
| Orcas Island | United States | ESD | More info |
| Orchid Island | Taiwan | KYD | More info |
| Ord River | Australia | ODR | More info |
| Ordaz | Mexico | PVR | More info |
| Orebro-bofors | Sweden | ORB | More info |
| Orel | Russian Federation | OEL | More info |
| Orenburg | Russian Federation | REN | More info |
| Orestes Acosta | Cuba | MOA | More info |
| Oria | Papua New Guinea | OTY | More info |
| Orientos | Australia | OXO | More info |
| Orinduik | Guyana | ORJ | More info |
| Orio Al Serio | Italy | BGY | More info |
| Oriximina | Brazil | ORX | More info |
| Orkney Island | United Kingdom | KOI | More info |
| Orland | Norway | OLA | More info |
| Orlando Executive | United States | ORL | More info |
| Orlando International | United States | MCO | More info |
| Orlando Sanford Intl | United States | SFB | More info |
| Orleans | France | ORE | More info |
| Orly | France | ORY | More info |
| Ormara | Pakistan | ORW | More info |
| Ormoc | Philippines | OMC | More info |
| Ornskoldsvik | Sweden | OER | More info |
| Oro Negro | Venezuela | CBS | More info |
| Orocue | Colombia | ORC | More info |
| Oroville | United States | OVE | More info |
| Orsk | Russian Federation | OSW | More info |
| Oruro | Bolivia | ORU | More info |
| Osage Beach | United States | OSB | More info |
| Oscar Reguera | Argentina | HOS | More info |
| Osh | Kyrgyzstan | OSS | More info |
| Oshakati | Namibia | OHI | More info |
| Oshawa | Canada | YOO | More info |
| Oshima | Japan | OIM | More info |
| Oshkosh | United States | OKS | More info |
| Osijek | Croatia (Hrvatska) | OSI | More info |
| Oskarshamn | Sweden | OSK | More info |
| Oslo - Gardermoen Airport | Norway | GEN | More info |
| Oslo Airport | Oslo | OSL | More info |
| Oslo Central Station | Norway | XZO | More info |
| Osmanabad | India | OMN | More info |
| Osmani International | Bangladesh | ZYL | More info |
| Ossima | Papua New Guinea | OSG | More info |
| Osvaldo Vieira | Guinea-Bissau | OXB | More info |
| Otis AFB | United States | FMH | More info |
| Otjiwarongo | Namibia | OTJ | More info |
| Otsego County | United States | GLR | More info |
| Ottawa International | Canada | YOW | More info |
| Otu | Colombia | OTU | More info |
| Ouadda | Central African Republic | ODA | More info |
| Ouagadougou | Burkina Faso | OUA | More info |
| Ouahigouya | Burkina Faso | OUG | More info |
| Ouanda Djalle | Central African Republic | ODJ | More info |
| Ouanga | Gabon | OUU | More info |
| Ouango Fitini | Cote D'Ivoire (Ivory Coast) | OFI | More info |
| Ouani | Comoros | AJN | More info |
| Ouarzazate | Morocco | OZZ | More info |
| Oudomxay | Laos | ODY | More info |
| Oudtshoorn | South Africa | OUH | More info |
| Oued Irara Apt | Algeria | HME | More info |
| Ouesso | Congo | OUE | More info |
| Oulu | Finland | OUL | More info |
| Oum Hadjer | Chad | OUM | More info |
| Ourilandia | Brazil | OIA | More info |
| Ourinhos | Brazil | OUS | More info |
| Outagamie County | United States | ATW | More info |
| Outer Skerries | United Kingdom | OUK | More info |
| Outlaw Field | United States | CKV | More info |
| Ouvea | New Caledonia | UVE | More info |
| Ouyen | Australia | OYN | More info |
| Ouzinkie SPB | United States | KOZ | More info |
| Ovalle | Chile | OVL | More info |
| Ovda | Israel | VDA | More info |
| Overberg (FAOB) | South Africa | OVG | More info |
| Owando | Congo | FTX | More info |
| Owatonna | United States | OWA | More info |
| Owen Roberts International | Cayman Islands | GCM | More info |
| Owendo | Gabon | OWE | More info |
| Owens Field | United States | CUB | More info |
| Oxford (Kidlington) | United Kingdom | OXF | More info |
| Oxford House | Canada | YOH | More info |
| Oyem | Gabon | OYE | More info |
| Ozona Municipal | United States | OZA | More info |