| OAG | Orange Regional Airport | Orange |  Australia |
| OAJ | Albert J Ellis Airport | Richlands |  United States of America |
| OAK | Metropolitan Oak International Airport | Oakland | United States of America |
| OAL | Cacoal Airport | Cacoal |  Brazil |
| OAM | Oamaru Airport | Timaru |  New Zealand |
| OAN | El Arrayan Airport/Olanchito Airport | La Ceiba |  Honduras |
| OAR | Marina Municipal Airport | Monterey | United States of America |
| OAX | Xoxocotlan Airport | Oaxaca |  Mexico |
| OBA | Oban Airport | Mount Isa | Australia |
| OBC | Obock Airport | Djibouti |  Djibouti |
| OBD | Obano Airport | Tembagapura |  Indonesia |
| OBE | Okeechobee County Airport | Vero Beach | United States of America |
| OBF | Oberpfaffenhofen Airport | Munich |  Germany |
| OBI | Obidos Airport | Santarem | Brazil |
| OBL | Zoersel Airport | Antwerp |  Belgium |
| OBM | Morobe Airport | Popondetta |  Papua New Guinea |
| OBN | Oban Airport / North Connel Airport | Campbeltown |  United Kingdom of Great Britain and Northern Ireland |
| OBO | Obihiro Airport | Obihiro |  Japan |
| OBS | Vals-Lanas Airport | Valence |  France |
| OBT | Oakland/Coliseum Stat Airport | Morgantown | United States of America |
| OBU | Kobuk/Wien Airport | Kobuk | United States of America |
| OBX | Obo Airport | Moro | Papua New Guinea |
| OBY | Ittoqqortoormiit Airport | Neerlerit Inaat |  Greenland |
| OCA | Ocean Reef Airport | Miami | United States of America |
| OCC | Francisco de Orellana Airport | Coca |  Ecuador |
| OCE | Ocean City Municipal Airport | Salisbury-Ocean City | United States of America |
| OCF | Ocala International Airport (Jim Taylor Field) | Gainesville | United States of America |
| OCH | A L Mangham Jr. Regional Airport | Longview | United States of America |
| OCI | Oceanic Airport | Anchorage | United States of America |
| OCJ | Ian Fleming International Airport | Kingston |  Jamaica |
| OCN | Oceanside Municipal Airport | San Diego | United States of America |
| OCV | Aguasclaras Airport | Cucuta |  Colombia |
| OCW | Warren Field Airport | Greenville | United States of America |
| ODA | Ouadda Airport | Bangui |  Central African Republic |
| ODB | Cordoba Airport | Cordoba |  Argentina |
| ODD | Oodnadatta Airport | Coober Pedy | Australia |
| ODE | Beldringe Airport | Aarhus |  Denmark |
| ODH | RAF Odiham | Southampton | United Kingdom of Great Britain and Northern Ireland |
| ODJ | Ouanda Djalle Airport | Bangui | Central African Republic |
| ODL | Cordillo Downs Airport | Longreach | Australia |
| ODN | Long Seridan Airport | Long Seridan |  Malaysia |
| ODO | Bodaybo Airport | Bodaybo |  Russian Federation |
| ODR | Ord River Airport | Kununurra | Australia |
| ODS | Odessa International Airport | Odessa |  Ukraine |
| ODW | A.J. Eisenberg Airport | Friday Harbor | United States of America |
| ODY | Oudomxai Airport | Oudomxay |  Lao People's Democratic Republic |
| OEA | Oneal Airport | Evansville | United States of America |
| OEC | Ocussi Airport | Atambua | Indonesia |
| OEL | Orel Airport | Kursk | Russian Federation |
| OEM | Vincent Fayks | Paramaribo |  Suriname |
| OEO | L.O. Simenstad Municipal Airport | Minneapolis | United States of America |
| OER | Ornskoldsvik Airport | Ornskoldsvik |  Sweden |
| OES | San Antonio Oeste Airport | Viedma | Argentina |
| OFI | Ouango Fitini Airport | Korhogo |  Cote d'Ivoire |
| OFJ | Olafsfjordur Airport | Akureyri |  Iceland |
| OFK | Stefan Field Airport | Sioux City | United States of America |
| OFU | Airstrip Airport | Pago Pago |  American Samoa |
| OGA | Searle Field Airport | North Platte | United States of America |
| OGB | Orangeburg Municipal Airport | Columbia | United States of America |
| OGD | Ogden-Hinckley Airport | Salt Lake City | United States of America |
| OGE | Ogeranang Airport | Lae | Papua New Guinea |
| OGG | Kahului Airport | Kahului | United States of America |
| OGL | Eugene F. Correira International Airport | Georgetown |  Guyana |
| OGN | Yonaguni Jima Airport | Ishigaki | Japan |
| OGO | Abengourou Airport | Abidjan | Cote d'Ivoire |
| OGR | Bongor Airport | Ndjamena |  Chad |
| OGS | Ogdensburg Airport | Ogdensburg | United States of America |
| OGV | Ongava Game Reserve Airport | Windhoek |  Namibia |
| OGX | Ain Beida Airport | Ouargla |  Algeria |
| OGZ | Vladikavkaz Airport | Vladikavkaz | Russian Federation |
| OHA | Royal Air Force Base Airport | Palmerston North | New Zealand |
| OHC | AFS | Savoonga | United States of America |
| OHD | Ohrid Airport | Ohrid |  Macedonia (the former Yugoslav Republic of) |
| OHH | Novostroyka Airport | Okha | Russian Federation |
| OHI | Oshakati Airport | Ondangwa | Namibia |
| OHO | Okhotsk Airport | Ust-Nera | Russian Federation |
| OHR | Wyk Auf Foehr Airport | Westerland | Germany |
| OHT | Kohat Airport | Peshawar |  Pakistan |
| OIA | Ourilandia | Carajas | Brazil |
| OIC | Eaton Airport | Binghamton | United Kingdom of Great Britain and Northern Ireland |
| OIL | Splane Memorial Airport | Franklin | United States of America |
| OIM | Oshima Airport | Tokyo | Japan |
| OIR | Okushiri Airport | Okushiri | Japan |
| OIT | Oita Airport | Oita | Japan |
| OJC | Johnson Executive Airport | Kansas City | United States of America |
| OKA | Naha Airport | Okinawa | Indonesia |
| OKB | Fraser Island Airport | Hervey Bay | Australia |
| OKC | Will Rogers World Airport | Oklahoma City | United States of America |
| OKE | Okino Erabu Airport | Yoronjima | Japan |
| OKF | Okaukuejo Airport | Ondangwa | Namibia |
| OKG | Okoyo Airport | Brazzaville |  Congo |
| OKH | RAF Cottesmore | Leicestershire | United Kingdom of Great Britain and Northern Ireland |
| OKI | Oki Island Airport | Yonago | Japan |
| OKJ | Okayama Airport | Okayama | Japan |
| OKK | Kokomo Airport | Indianapolis | United States of America |
| OKL | Oksibil Airport | Wamena | Indonesia |
| OKM | Okmulgee Regional Airport | Tulsa | United States of America |
| OKN | Okondja Airport | Libreville |  Gabon |
| OKO | Yokota Air Base | Tokyo | Japan |
| OKP | Oksapmin Airport | Tari | Papua New Guinea |
| OKQ | Okaba Airport | Merauke | Indonesia |
| OKR | Yorke Island Airport | Horn Island | Australia |
| OKS | Oshkosh Airport | Alliance | United States of America |
| OKT | Oktiabrskij Airport | Bugulma | Russian Federation |
| OKU | Mokuti Lodge Airport | Ondangwa | Namibia |
| OKV | Okao | Tabubil | Papua New Guinea |
| OKY | Oakey Airport | Brisbane | Australia |
| OLA | Orland Airport | Trondheim |  Norway |
| OLB | Costa Smeralda Airport | Olbia |  Italy |
| OLD | Old Town Airport | Bangor | United States of America |
| OLE | Cattaraugus County-Olean Airport | Bradford | United States of America |
| OLF | L. M. Clayton Airport | Wolf Point | United States of America |
| OLH | Old Harbor SPB | Old Harbor | United States of America |
| OLI | Rif Airport | Nuiqsut | Iceland |
| OLJ | Olpoi Airport | Espiritu Santo |  Vanuatu |
| OLK | Fuerte Olimpo Airport | Asuncion |  Paraguay |
| OLM | Olympia Regional Airport | Seattle | United States of America |
| OLN | Colonia Sarmiento Airport | Comodoro Rivadavia | Argentina |
| OLO | Olomouc Airport | Brno |  Czechia |
| OLP | Olympic Dam Airport | Olympic Dam | Australia |
| OLQ | Olsobip Airport | Tabubil | Papua New Guinea |
| OLS | Nogales International Airport | Tucson | United States of America |
| OLU | Columbus Municipal Airport | Lincoln | United States of America |
| OLV | Olive Branch Airport | Memphis | United States of America |
| OLY | Olney-Noble Airport | Evansville | United States of America |
| OMA | Eppley Airfield Airport | Omaha | United States of America |
| OMB | Omboue Airport | Libreville | Gabon |
| OMC | Ormoc Airport | Tacloban |  Philippines |
| OMD | Oranjemund Airport | Oranjemund | Namibia |
| OME | Nome Airport | Nome | United States of America |
| OMF | King Hussein Airport | Amman |  Jordan |
| OMG | Omega Airport | Windhoek | Namibia |
| OMH | Urmieh Airport | Nazluy-ye Jonubi |  Iran (Islamic Republic of) |
| OMI | Omidiyeh Air Base | Bandar Mahshahr | Iran (Islamic Republic of) |
| OMJ | Omura Airport | Nagasaki | Japan |
| OMK | Municipal Airport | Wenatchee | United States of America |
| OML | Omkalai Airport | Goroka | Papua New Guinea |
| OMM | Marmul Airport | Salalah |  Oman |
| OMN | Osmanabad Airport | Aurangabad |  India |
| OMO | Mostar Airport | Mostar |  Bosnia and Herzegovina |
| OMR | Oradea Airport | Oradea |  Romania |
| OMS | Omsk Airport | Omsk | Russian Federation |
| OMY | Thbeng Meanchey Airport (Preah Vinhear Airport) | Siem Reap |  Cambodia |
| ONA | Winona Municipal Airport (Max Conrad Field) | La Crosse | United States of America |
| ONB | Ononge Airport | Port Moresby | Papua New Guinea |
| OND | Ondangwa Airport | Ondangwa | Namibia |
| ONE | Onepusu Airport | Honiara |  Solomon Islands |
| ONG | Mornington Airport | Mornington | Australia |
| ONH | Oneonta Municipal Airport | Binghamton | United States of America |
| ONI | Moanamani Airport | Tembagapura | Indonesia |
| ONJ | Odate Noshiro Airport | Odate Noshiro | Japan |
| ONL | O Neill Municipal Airport (John L. Baker Field) | Grand Island | United States of America |
| ONM | Socorro Airport | Albuquerque | United States of America |
| ONN | Onion Bay Airport | Port Williams | United States of America |
| ONO | Ontario Municipal Airport | Boise | United States of America |
| ONP | Newport Municipal Airport | Eugene | United States of America |
| ONQ | Zonguldak Airport | Izmit |  Turkey |
| ONR | Monkira Airport | Winton | Australia |
| ONS | Onslow Airport | Onslow | Australia |
| ONT | Ontario International Airport | Ontario | United States of America |
| ONU | Ono I Lau Airport | Nuku'alofa |  Fiji |
| ONX | Enrique Adolfo Jimenez Airport | Balboa |  Panama |
| ONY | Olney Airport | Wichita Falls | United States of America |
| OOA | Oskaloosa Municipal Airport | Cedar Rapids | United States of America |
| OOK | Toksook Bay Airport | Toksook Bay | United States of America |
| OOL | Gold Coast (coolangatta) Airport | Coolangatta (Gold Coast) | Australia |
| OOM | Cooma Airport | Cooma | Australia |
| OOR | Mooraberree Airport | Winton | Australia |
| OOT | Onotoa Airport | Tarawa |  Kiribati |
| OPA | Kopasker Airport | Akureyri | Iceland |
| OPB | Open Bay Airport | Rabaul | Papua New Guinea |
| OPI | Oenpelli Airport | Maningrida | Australia |
| OPL | St Landry Parish Airport | Lafayette | United States of America |
| OPO | Francisco Sa Carneiro Airport | Porto |  Portugal |
| OPS | Sinop Airport | Sinop | Brazil |
| OPU | Balimo Airport | Daru | Papua New Guinea |
| OPW | Opuwa Airport | Ondangwa | Namibia |
| ORA | Oran Airport | Jujuy | Argentina |
| ORB | Orebro-bofors Airport | Orebro | Sweden |
| ORC | Orocue Airport | El Yopal | Colombia |
| ORD | Chicago O'hare International | Chicago | United States of America |
| ORE | Orleans Airport | Paris | France |
| ORF | Norfolk International Airport | Norfolk | United States of America |
| ORG | Zorg En Hoop | Paramaribo | Suriname |
| ORH | Worcester Regional Airport | Worcester | United States of America |
| ORI | Port Lions SPB | Port Lions | United States of America |
| ORJ | Orinduik Airport | Georgetown | Guyana |
| ORK | Cork Airport | Cork |  Ireland |
| ORL | Orlando Executive Airport | Orlando | United States of America |
| ORM | Sywell Aerodrome | Milton Keynes | United Kingdom of Great Britain and Northern Ireland |
| ORN | Oran Es-Senia – Ahmed Ben Bella Airport | Oran | Algeria |
| ORO | Yoro Airport | La Ceiba | Honduras |
| ORP | Orapa Airport | Francistown |  Botswana |
| ORR | Yorketown Airport | Kingscote | Australia |
| ORS | Waterport Airport | Palm Island | Australia |
| ORT | Northway Airport | Yakutat | United States of America |
| ORU | Oruro Airport | Cochabamba |  Bolivia (Plurinational State of) |
| ORV | Curtis Memorial Airport | Noorvik | United States of America |
| ORW | Ormara Airport | Turbat | Pakistan |
| ORX | Oriximina Airport | Santarem | Brazil |
| ORY | Orly | Paris | France |
| ORZ | Orange Walk Airport | Belize City |  Belize |
| OSB | Osage Beach Airport | Fort Leonard Wood | United States of America |
| OSC | Oscoda–Wurtsmith Airport | Alpena | United States of America |
| OSD | Åre Östersund Airport | Ostersund | Sweden |
| OSE | Omora Airport | Lae | Papua New Guinea |
| OSG | Ossima Airport | Vanimo | Papua New Guinea |
| OSH | Wittman Regional Airport | Appleton | United States of America |
| OSI | Osijek Airport | Osijek |  Croatia |
| OSK | Oskarshamn Airport | Kalmar | Sweden |
| OSL | Gardermoen Airport | Oslo | Norway |
| OSM | Mosul Airport | Erbil |  Iraq |
| OSN | Osan AB | Seoul |  Korea (Republic of) |
| OSP | Redzikowo Airport | Gdansk |  Poland |
| OSR | Mosnov Airport | Ostrava | Czechia |
| OSS | Osh International Airport | Osh |  Kyrgyzstan |
| OST | Ostend/Bruges International Airport | Bruges | Belgium |
| OSU | Ohio State University | Columbus | United States of America |
| OSW | Orsk Airport | Orsk | Russian Federation |
| OSX | Attala County Airport | Jackson | United States of America |
| OSY | Namsos Airport | Namsos | Norway |
| OSZ | Koszalin Airport | Poznan | Poland |
| OTA | Mota Airport | Bahar Dar |  Ethiopia |
| OTC | Bol-Berim Airport | Ndjamena | Chad |
| OTD | Contadora Airport | Panama City | Panama |
| OTG | Worthington Airport | Sioux Falls | United States of America |
| OTH | North Bend Airport | North Bend | United States of America |
| OTI | Pitu Airport | Ternate | Indonesia |
| OTJ | Otjiwarongo Airport | Windhoek | Namibia |
| OTL | Boutilimit Airport | Nouakchott |  Mauritania |
| OTM | Ottumwa Regional Airport | Kirksville | United States of America |
| OTN | Ed-Air Airport | Evansville | United States of America |
| OTO | Vor Airport | Albuquerque | United States of America |
| OTP | Henri Coanda International Airport | Bucharest | Romania |
| OTR | Coto 47 Airport | Golfito |  Costa Rica |
| OTS | Anacortes Airport | Bellingham | United States of America |
| OTU | Otu Airport | Barrancabermeja | Colombia |
| OTV | Ontong Java Airport | Fera Island | Solomon Islands |
| OTY | Oria Airport | Rabaul | Papua New Guinea |
| OTZ | Kotzebue Airport | Kotzebue | United States of America |
| OUA | Ouagadougou Airport | Ouagadougou |  Burkina Faso |
| OUD | Les Anglades Airport | Oujda |  Morocco |
| OUE | Ouesso Airport | Brazzaville | Congo |
| OUG | Ouahigouya Airport | Ouagadougou | Burkina Faso |
| OUH | Oudtshoorn Airport | George |  South Africa |
| OUI | Ban Houei Airport | Luang Namtha | Lao People's Democratic Republic |
| OUK | Outer Skerries Airport | Shetland Islands | United Kingdom of Great Britain and Northern Ireland |
| OUL | Oulu Airport | Oulu |  Finland |
| OUM | Oum Hadjer Airport | Ndjamena | Chad |
| OUN | Max Westheimer Airport | Oklahoma City | United States of America |
| OUR | Batouri Airport | Yaounde |  Cameroon |
| OUS | Ourinhos Airport | Marilia | Brazil |
| OUT | Bousso Airport | Ndjamena | Chad |
| OUU | Ouanga Airport | Libreville | Gabon |
| OUZ | Zouerate Airport | Nouadhibou | Mauritania |
| OVA | Bekily Airport | Fort Dauphin |  Madagascar |
| OVB | Tolmachevo Airport | Novosibirsk | Russian Federation |
| OVD | Asturias Airport | Asturias |  Spain |
| OVE | Oroville Airport | Chico | United States of America |
| OVG | Overberg (FAOB) | Cape Town | South Africa |
| OVL | Ovalle Airport | La Serena |  Chile |
| OVR | Olavarria Airport | Bahia Blanca | Argentina |
| OVS | Sovetskiy Airport | Sovetsky | Russian Federation |
| OWA | Owatonna Airport | Rochester | United States of America |
| OWB | Daviess County Airport | Owensboro | United States of America |
| OWD | Norwood Memorial Airport | Boston | United States of America |
| OWE | Owendo Airport | Libreville | Gabon |
| OWK | Central Maine Airport of Norridgewock | Augusta | United States of America |
| OXB | Osvaldo Vieira International Airport | Bissau |  Guinea-Bissau |
| OXC | Waterbury-oxford Airport | New Haven | United States of America |
| OXD | Miami University Airport | Cincinnati | United States of America |
| OXF | Oxford (Kidlington) Airport | Montgomery | United States of America |
| OXO | Orientos Airport | Broken Hill | Australia |
| OXR | Ventura Airport | Santa Barbara | United States of America |
| OXY | Morney Airport | Winton | Australia |
| OYA | Goya Airport | Resistencia | Argentina |
| OYE | Oyem Airport | Libreville | Gabon |
| OYG | Moyo Airport | Entebbe |  Uganda |
| OYK | Oiapoque Airport | Macapa | Brazil |
| OYL | Moyale Lower Airport | Wajir |  Kenya |
| OYN | Ouyen Airport | Mildura | Australia |
| OYO | Tres Arroyos Airport | Bahia Blanca | Argentina |
| OYP | St-Georges de lOyapock Airport | Cayenne |  French Guiana |
| OYS | Yosemite Ntl Park Airport | Mammoth Lakes | United States of America |
| OZA | Ozona Municipalcipal Airport | Del Rio | United States of America |
| OZC | Labo Airport | Ozamis City | Philippines |
| OZH | Zaporozhye Airport | Zaporozhye | Ukraine |
| OZP | Moron Air Base | Sevilla | Spain |
| OZR | Cairns Army Airfield | Dothan | United States of America |
| OZU | Montilla Airport | Puente Genil | Spain |
| OZZ | Ouarzazate Airport | Ouarzazate | Morocco |