| IATA | ICAO | Airport name | Location |
|---|
| OAJ | KOAJ | Albert J. Ellis Airport | Jacksonville, North Carolina, United States |
| OAK | KOAK | Oakland International Airport | Oakland (near San Francisco), California, United States |
| OAM | NZOU | Oamaru Airport | Oamaru, North Otago, New Zealand |
| OAR | KOAR | Marina Municipal Airport | Marina, California, United States |
| OAX | MMOX | Xoxocotlán International Airport | Oaxaca, Mexico |
| OBC | HDOB | Obock | Djibouti |
| OBD | LEBA | Córdoba Airport | Córdoba, Spain |
| OBE | KOBE | Okeechobee County Airport | Okeechobee, Florida, United States |
| OBO | RJCB | Tokachi-Obihiro Airport | Obihiro, Tokachi Subprefecture, Hokkaido, Japan |
| OBU | | Kobuk Airport | Kobuk, Alaska, United States |
| OCA | | Ocean Reef Club Airport | Key Largo, Florida, United Sates |
| OCC | SECO | Francisco de Orellana Airport | El Coca, Ecuador |
| OCE | KOXB | Ocean City Municipal Airport | Ocean City, Maryland, United States |
| OCF | KOCF | Ocala International Airport (Jim Taylor Field) | Ocala, Florida, United States |
| OCH | KOCH | A. L. Mangham Jr. Regional Airport | Nacogdoches, Texas, United States |
| OCJ | MKBS | Boscobel Aerodrome | Ocho Rios, Jamaica |
| OCN | KOKB | Oceanside Municipal Airport | Oceanside, California, United States |
| OCQ | KOCQ | J. Douglas Bake Memorial Airport | Oconto, Wisconsin, United States |
| OCW | KOCW | Warren Field | Washington, North Carolina, United States |
| ODE | EKOD | Odense Airport | Odense, Denmark |
| ODH | EGVO | RAF Odiham | Odiham, United Kingdom |
| ODO | KODO | Odessa-Schlemeyer Field | Odessa, Texas, United States |
| ODS | UKOO | Odessa International Airport | Odessa, Ukraine |
| ODX | KODX | Evelyn Sharp Field | Ord, Nebraska, United States |
| OEA | KOEA | O'Neal Airport | Vincennes, Indiana, United States |
| OEB | KOEB | Branch County Memorial Airport | Coldwater, Michigan, United States |
| OEL | KOEL | Oakley Municipal Airport | Oakley, Kansas, United States |
| OEM | SMPA | Vincent Fayks Airport | Paloemeu, Suriname |
| OEO | KOEO | L. O. Simenstad Municipal Airport | Osceola, Wisconsin, United States |
| OER | ESNO | Örnsköldsvik Airport | Örnsköldsvik, Sweden |
| OFF | KOFF | Offutt AFB | Omaha, Nebraska, United States |
| OFK | KOFK | Karl Stefan Memorial Airport | Norfolk, Nebraska, United States |
| OFP | KOFP | Hanover County Municipal Airport | Richmond/Ashland, Virginia, United States |
| OFU | | Ofu Airport | Ofu, American Samoa |
| OGA | KOGA | Searle Field | Ogallala, Nebraska, United States |
| OGB | KOGB | Orangeburg Municipal Airport | Orangeburg, South Carolina, United States |
| OGD | KOGD | Ogden-Hinckley Airport | Ogden, Utah, United States |
| OGG | PHOG | Kahului Airport | Kahului, Hawaii, United States |
| OGL | SYGO | Ogle Airport | Georgetown, Guyana |
| OGM | KOGM | Ontonagon County Airport | Ontonagon, Michigan, United States |
| OGR | FTTB | Bongor Airport | Bongor, Chad |
| OGS | KOGS | Ogdensburg International Airport | Ogdensburg, New York, United States |
| OHD | LWOH | Ohrid Airport | Ohrid, Republic of Macedonia |
| OHH | | Okha Airport | Okha, Russia |
| OHT | OPKT | Kohat Airport | Kohat, Pakistan |
| OIC | KOIC | Lt. Warren Eaton Airport | Norwich, New York, United States |
| OIN | KOIN | Oberlin Municipal Airport | Oberlin, Kansas, United States |
| OIR | RJEO | Okushiri Airport | Okushiri, Okushiri Island, Hokkaido, Japan |
| OIT | RJFO | Oita Airport | Oita, Japan |
| OJA | KOJA | Thomas P. Stafford Airport | Weatherford, Oklahoma, United States |
| OJC | KOJC | Johnson County Executive Airport | Olathe, Kansas, United States |
| OKA | ROAH | Naha Airport | Okinawa, Japan |
| OKB | | Orchid Beach | Fraser Island, Queensland,Australia |
| OKC | KOKC | Will Rogers World Airport | Oklahoma City, Oklahoma, United States |
| OKJ | RJOB | Okayama Airport | Okayama, Japan |
| OKK | KOKK | Kokomo Municipal Airport | Kokomo, Indiana, United States |
| OKM | KOKM | Okmulgee Regional Airport | Okmulgee, Oklahoma, United States |
| OKS | KOKS | Garden County Airport | Oshkosh, Nebraska, United States |
| OKZ | KOKZ | Kaolin Field | Sandersville, Georgia, United States |
| OLB | LIEO | Olbia-Costa Smeralda Airport | Olbia, Italy |
| OLD | KOLD | Old Town Municipal Airport and Seaplane Base (DeWitt Field) | Old Town, Maine, United States |
| OLE | KOLE | Cattaraugus County-Olean Airport | Olean, New York, United States |
| OLF | KOLF | L. M. Clayton Airport | Wolf Point, Montana, United States |
| OLG | KOLG | Solon Springs Municipal Airport | Solon Springs, Wisconsin, United States |
| OLH | | Old Harbor Airport | Old Harbor, Alaska, United States |
| OLM | KOLM | Olympia Airport | Olympia, Washington, United States |
| OLS | KOLS | Nogales International Airport | Nogales, Arizona, United States |
| OLU | KOLU | Columbus Municipal Airport (Nebraska) | Columbus, Nebraska, United States |
| OLV | KOLV | Olive Branch Airport | Olive Branch, Mississippi, United States |
| OLY | KOLY | Olney-Noble Airport | Olney-Noble, Illinois, United States |
| OLZ | KOLZ | Oelwein Municipal Airport | Oelwein, Iowa, United States |
| OMA | KOMA | Eppley Airfield | Omaha, Nebraska, United States |
| OME | PAOM | Nome Airport | Nome, Alaska, United States |
| OMH | KOMH | Orange County Airport | Orange, Virginia, United States |
| OMI | OIAJ | Omidiyeh Air Base | Omidiyeh, Iran |
| OMK | KOMK | Omak Airport | Omak, Washington, United States |
| OMN | | Osmanabad Airport | Osmanabad, India |
| OMR | LROD | Oradea International Airport | Oradea, Romania |
| OMS | UNOO | Omsk Airport | Omsk, Russia |
| ONA | KONA | Winona Municipal Airport (Max Conrad Field) | Winona, Minnesota, United States |
| ONJ | RJSR | Odate-Noshiro Airport | Kitaakita, Akita, Japan |
| ONL | KONL | The O'Neill Municipal Airport (John L. Baker Field) | O'Neill, Nebraska, United States |
| ONM | KONM | Socorro Municipal Airport | Socorro, New Mexico, United States |
| ONO | KONO | Ontario Municipal Airport | Ontario, Oregon, United States |
| ONP | KONP | Newport Municipal Airport | Newport, Oregon, United States |
| ONT | KONT | Ontario International Airport | Ontario (near Los Angeles), California, United States |
| ONX | MPEJ | Enrique Adolfo Jiménez Airport | Colón, Panama |
| ONY | KONY | Olney Municipal Airport | Olney, Texas, United States |
| ONZ | KONZ | Grosse Ile Municipal Airport | Detroit/Grosse Ile, Michigan, United States |
| OOA | KOOA | Oskaloosa Municipal Airport | Oskaloosa, Iowa, United States |
| OOK | PAOO | Toksook Bay Airport | Toksook Bay, Alaska, United States |
| OOL | YBCG | Gold Coast Airport | Coolangatta, Queensland, Australia |
| OPF | KOPF | Opa-locka Airport | Miami, Florida, United States |
| OPL | KOPL | St. Landry Parish Airport (Ahart Field) | Opelousas, Louisiana, United States |
| OPN | KOPN | Thomaston-Upson County Airport | Thomaston, Georgia, United States |
| OPO | LPPR | Francisco Sá Carneiro Airport | Porto, Portugal |
| OQN | KOQN | Brandywine Airport | West Chester, Pennsylvania, United States |
| OQU | KOQU | Quonset State Airport | North Kingstown, Rhode Island, United States |
| OQW | KOQW | Maquoketa Municipal Airport | Maquoketa, Iowa, United States |
| ORB | ESOE | Örebro Airport | Örebro, Sweden |
| ORC | KORC | Orange City Municipal Airport | Orange City, Iowa, United States |
| ORD | KORD | O'Hare International Airport (formerly Orchard Depot Field) | Chicago, Illinois, United States |
| ORE | KORE | Orange Municipal Airport | Orange, Massachusetts, United States |
| ORF | KORF | Norfolk International Airport | Norfolk, Virginia (near Virginia Beach and Williamsburg), United States |
| ORG | KORG | Orange County Airport (Texas) | Orange, Texas, United States |
| ORG | SMZO | Zorg en Hoop Airport | Paramaribo, Suriname |
| ORH | KORH | Worcester Regional Airport | Worcester, Massachusetts, United States |
| ORI | KORI | Port Lions Airport | Port Lions, Alaska, United States |
| ORJ | SYDR | Orinduik Airport | Orinduik, Guyana |
| ORK | EICK | Cork International Airport | Cork, Ireland |
| ORL | KORL | Orlando Executive Airport | Orlando, Florida, United States |
| ORM | EGBK | Sywell Aerodrome | Northampton / Peterborough, United Kingdom |
| ORS | | Waterport Airport | Orpheus, Queensland, Australia |
| ORT | PAOR | Northway Airport | Northway, Alaska, United States |
| ORV | PFNO | Robert (Bob) Curtis Memorial Airport (FAA: D76) | Noorvik, Alaska, United States |
| ORY | LFPO | Orly International Airport | Paris-Orly, Paris, France |
| OSA | | All Airports | Osaka, Japan |
| OSC | KOSC | Oscoda-Wurtsmith Airport | Oscoda, Michigan, United States |
| OSD | ESNZ | Åre Östersund Airport | Östersund, Sweden |
| OSH | KOSH | Wittman Regional Airport | Oshkosh, Wisconsin, United States |
| OSL | ENGM | Oslo Airport, Gardermoen | Ullensaker (near Oslo), Norway |
| OSR | LKMT | Ostrava-Mosnov International Airport | Ostrava, Czech Republic |
| OSS | UAFO | Osh Airport | Osh, Kyrgyzstan |
| OST | EBOS | Ostend-Bruges International Airport | Flanders, Belgium |
| OSU | KOSU | Ohio State University Airport | Columbus, Ohio, United States |
| OSX | KOSX | Kosciusko-Attala County Airport | Kosciusko, Mississippi, United States |
| OSY | ENNM | Namsos Airport, Høknesøra | Namsos, Norway |
| OTC | FTTL | Bol Airport | Bol, Chad |
| OTG | KOTG | Worthington Municipal Airport | Worthington, Minnesota, United States |
| OTH | KOTH | North Bend Municipal Airport | North Bend, Oregon, United States |
| OTL | GQNB | Boutilimit Airport | Boutilimit, Mauritania |
| OTM | KOTM | Ottumwa Industrial Airport | Ottumwa, Iowa, United States |
| OTN | KOTN | Ed-Air Airport | Oaktown, Indiana, United States |
| OTP | LROP | Henri Coanda International Airport | Otopeni (near Bucharest), Romania |
| OTR | MRCC | Coto 47 Airport | Coto 47, Costa Rica |
| OTZ | PAOT | Ralph Wien Memorial Airport | Kotzebue, Alaska, United States |
| OUA | DFFD | Ouagadougou Airport | Ouagadougou, Burkina Faso |
| OUD | GMFO | Oujda Angads Airport | Oujda, Morocco |
| OUG | DFCC | Ouahigouya Airport | Ouahigouya, Burkina Faso |
| OUL | EFOU | Oulu Airport | Oulu, Finland |
| OUM | | Oum Hadjer Airport | Oum Hadjer, Chad |
| OUN | KOUN | University of Oklahoma Westheimer Airport | Norman, Oklahoma, United States |
| OUR | FKKI | Batouri Airport | Batouri, Cameroon |
| OUT | FTTS | Bousso Airport | Bousso, Chad |
| OUZ | GQPZ | Tazadit Airport | Zouerate, Mauritania |
| OVB | UNNT | Novosibirsk Tolmachevo Airport | Novosibirsk, Russia |
| OVD | LEAS | Asturias Airport (Oviedo Airport) | Oviedo, Asturias, Spain |
| OVE | KOVE | Oroville Municipal Airport | Oroville, California, United States |
| OVL | KOVL | Olivia Regional Airport | Olivia, Minnesota, United States |
| OVO | KOVO | North Vernon Airport | North Vernon, Indiana, United States |
| OWA | KOWA | Owatonna Degner Regional Airport | Owatonna, Minnesota, United States |
| OWB | KOWB | Owensboro-Daviess County Airport | Owensboro, Kentucky, United States |
| OWD | KOWD | Norwood Memorial Airport | Norwood, Massachusetts, United States |
| OWI | KOWI | Ottawa Municipal Airport | Ottawa, Kansas, United States |
| OWK | KOWK | Central Maine Airport of Norridgewock | Norridgewock, Maine, United States |
| OWX | KOWX | Putnam County Airport | Ottawa, Ohio, United States |
| OXB | GGOV | Osvaldo Vieiro International Airport | Bissau, Guinea-Bissau |
| OXC | KOXC | Waterbury-Oxford Airport | Oxford, Connecticut, United States |
| OXD | KOXD | Miami University Airport | Oxford, Ohio, United States |
| OXI | KOXI | Starke County Airport | Knox, Indiana, United States |
| OXR | KOXR | Oxnard Airport | Oxnard, California, United States |
| OXV | KOXV | Knoxville Municipal Airport | Knoxville, Iowa, United States |
| OYK | SBOI | Oiapoque Airport | Oiapoque, Amapa, Brasil |
| OZA | KOZA | Ozona Municipal Airport | Ozona, Texas, United States |
| OZC | RPMO | Labo Airport | Ozamiz City, Philippines |
| OZR | KOZR | Cairns Army Airfield (Fort Rucker) | Fort Rucker/Ozark, Alabama, United States |
| OZW | KOZW | Livingston County Airport | Howell, Michigan, United States |
| OZZ | GMMZ | Ouarzazate Airport | Ouarzazate, Morocco |