| City/Airport Name | Country | Airport Code | |
| OAK HARBOR | USA | ODW | USA (WA) |
| OAKLAND INTERNATIONAL | USA | OAK | USA (CALIFORNIA) |
| OAMARU | New Zealand | OAM | |
| OAXACA | Mexico | OAX | |
| OBANO | Indonesia | OBD | |
| OBERPFAFFENHOFEN | Germany | OBF | |
| OBIHIRO | Japan | OBO | |
| OBO | Papua New Guinea | OBX | |
| OBO M'BOKI | | MKI | CENTRAL AFRICAN REP. |
| OBOCK | Djibouti | OBC | |
| OCANA | Colombia | OCV | |
| OCEAN REEF | USA | OCA | USA (FLORIDA) |
| OCHO RIOS BOSCOBEL | Jamaica | OCJ | |
| OCUSSI | Indonesia | OEC | |
| ODENSE BELDRINGE | Denmark | ODE | |
| ODESSA TSNTRALNY | Ukraine | ODS | |
| ODIENNE | Ivory Coast | KEO | |
| OFU | Samoa (Western) | OFU | SAMOA |
| OGDENSBURG | USA | OGS | USA (NEW YORK) |
| OHRID | Macedonia | OHD | FORMER MACEDONIA |
| OITA | Japan | OIT | |
| OKABA | Indonesia | OKQ | |
| OKAUKUEJO | Namibia | OKF | |
| OKAYAMA | Japan | OKJ | |
| OKI ISLAND | Japan | OKI | |
| OKINAWA NAHA | Japan | OKA | |
| OKINU ERABU | Japan | OKE | |
| OKLAHOMA CITY WILL ROGER WORLD | USA | OKC | USA (OKLAHOMA) |
| OKONDJA | Gabon | OKN | |
| OKSAPMIN | Papua New Guinea | OKP | |
| OKSIBIL | Indonesia | OKL | |
| OKUSHIRI | Japan | OIR | |
| OLAFSFJORDUR | Iceland | OFJ | |
| OLBIA COSTA SMERALDA | Italy | OLB | |
| OLD CROW | Canada | YOC | CANADA (YT) |
| OLD HARBOR | USA | OLH | USA (ALASKA) |
| OLGA BAY | USA | KOY | USA (ALASKA) |
| OLPOI | Vanuatu | OLJ | |
| OLSOBIP | Papua New Guinea | OLQ | |
| OLYMPIA | USA | OLM | USA (WASHINGTON) |
| OLYMPIC DAM | Australia | OLP | AUSTRALIA (SA) |
| OMAHA EPPLEY AIRFIELD | USA | OMA | |
| OMBOUE HOSPIAL | Gabon | OMB | |
| OMSK | Russia | OMS | |
| ONDANGWA | Namibia | OND | |
| ONOTOA | Kiribati | OOT | |
| ONSLOW | Australia | ONS | AUSTRALIA (WA) |
| ONTARIO INTERNATIONAL | USA | ONT | USA (CALIFORNIA) |
| ORADEA | Romania | OMR | |
| ORAN ES SENIA | Algeria | ORN | |
| ORANGE SPRINGHILL | Australia | OAG | AUSTRALIA (NSW) |
| ORANJEMUND | Namibia | OMD | |
| ORAPA | Botswana | ORP | |
| ORBOST | Australia | RBS | AUSTRALIA (VI) |
| ORCHID ISLAND | Taiwan | KYD | TAIWAN |
| ORDZHONIKIDZE | Russia | OGZ | |
| OREBRO | Sweden | ORB | |
| ORENBURG CENTRAL | Russia | REN | |
| ORLANDO EXECUTIVE | USA | ORL | USA (FLORIDA) |
| ORLANDO INTERNATIONAL | USA | MCO | USA (FLORIDA) |
| ORMARA MIL. & CIVIL | Pakistan | ORW | |
| ORNSKOLDSVIK | Sweden | OER | |
| OROCUE | Colombia | ORC | |
| ORSTA-VOLDA HOVDEN | Norway | HOV | |
| OSAKA INTERNATIONAL | Japan | OSA | |
| OSAKA KANSAI INTERNATIONAL | Japan | KIX | |
| OSH | Russia | OSS | |
| OSHAKATI | Namibia | OHI | |
| OSHAWA | Canada | YOO | CANADA (ONTARIO) |
| OSHIMA | Japan | OIM | |
| OSKARSHAMN | Sweden | OSK | |
| OSKOSH WITTMAN REGIONAL | USA | OSH | USA (WI) |
| OSLO FORNEBU | Norway | FBU | |
| OSLO GARDERMOEN | Norway | GEN | |
| OSLO LUFTHAVN | Norway | OSL | |
| OSORNO CANAL BAJO HOTT | Chile | ZOS | |
| OSTEND | Belgium | OST | |
| OSTERSUND FROSON | Sweden | OSD | |
| OTTAWA ROCKCLIFFE | Canada | YRO | CANADA (ONTARIO) |
| OTTAWA UPLANDS INTERNATIONAL | Canada | YOW | CANADA (ONTARIO) |
| OTTUMWA | USA | OTM | USA (IA) |
| OTU OTU | Colombia | OTU | |
| OUADDA | | ODA | CENTRAL AFRICAN REP. |
| OUAGADOUGOU INTERNATIONAL | Burkina Faso | OUA | |
| OUAHIGOUYA | Burkina Faso | OUG | |
| OUANDA-DJALLE | | ODJ | CENTRAL AFRICAN REP. |
| OUANGO FITINI | Ivory Coast | OFI | |
| OUARGLA | Algeria | OGX | |
| OUARZAZATE | Morocco | OZZ | |
| OUDOMXAY | Laos | ODY | |
| OUESSO | Congo, Democratic Republic of | OUE | CONGO |
| OUJDA ANGADS | Morocco | OUD | |
| OULU | Finland | OUL | |
| OUM HADJER | Chad | OUM | TCHAD |
| OURINHOS | Brazil | OUS | BRAZIL (SP) |
| OUVEA OULOUP | New Caledonia | UVE | NEW CALEDONIA (F) |
| OUZINKIE | USA | KOZ | USA (ALASKA) |
| OVDA OVDA | Israel | VDA | |
| OWANDO | Congo, Democratic Republic of | FTX | CONGO |
| OWENSBORO | USA | OWB | USA (KENTUCKY) |
| OXFORD HOUSE | Canada | YOH | CANADA (MANITOBA) |
| OXNARD-VENTURA COUNTY | USA | OXR | USA (CALIFORNIA) |
| OYEM | Gabon | OYE | |
