| OAA | Air Base | Shank | AF |
| OAG | Orange Airport | Orange | AU |
| OAH | Shindand Air Base | Shindand | AF |
| OAI | Bagram Airport | Bagram | AF |
| OAJ | Albert J Ellis Airport | Jacksonville | US |
| OAK | Metropolitan Oakland International Airport | Oakland | US |
| OAL | Cacoal Airport | Cacoal | BR |
| OAM | Oamaru Airport | Oamaru | NZ |
| OAN | Olanchito Airport | Olanchito | HN |
| OAR | Fritzche Army Air Field | Monterey | US |
| OAS | Air Base | Sharana | AF |
| OAX | Xoxocotlan Airport | Oaxaca | MX |
| OAZ | Camp Bastion | Camp Bastion | AF |
| OBA | Oban Airport | Oban | AU |
| OBC | Obock Airport | Obock | DJ |
| OBD | Obano Airport | Obano | ID |
| OBE | Okeechobee County Airport | Okeechobee | US |
| OBF | Oberpfaffenhofen Airport | Oberpfaffenhofen | DE |
| OBI | Obidos Airport | Obidos | BR |
| OBK | Sky Harbor Airport | Northbrook | US |
| OBL | Oostmalle Airport | Zoersel | BE |
| OBM | Morobe Airport | Morobe | PG |
| OBN | North Connel Airport | Oban | GB |
| OBO | Obihiro Airport | Obihiro | JP |
| OBS | Vals-Lanas Airport | Aubenas | FR |
| OBT | Oakland/Coliseum Station | Oakland | US |
| OBU | Kobuk/Wien Airport | Kobuk | US |
| OBX | Obo Airport | Obo | PG |
| OBY | Heliport | Ittoqqortoormiit | GL |
| OBZ | Bus Station | Hamburg | DE |
| OCA | Ocean Reef Airport | Ocean Reef | US |
| OCC | Coca Airport | Coca | EC |
| OCE | Ocean City Municipal Airport | Ocean City | US |
| OCF | Taylor Field | Ocala | US |
| OCH | Nacogdoches Airport | Nacogdoches | US |
| OCI | Oceanic Airport | Oceanic | US |
| OCJ | Boscobel Airport | Ocho Rios | JM |
| OCM | Boolgeeda Airport | Boolgeeda | AU |
| OCN | Oceanside Municipal Airport | Oceanside | US |
| OCV | Aguasclaras Airport | Ocana | CO |
| OCW | Warren Field | Washington | US |
| ODA | Ouadda Airport | Ouadda | CF |
| ODB | Cordoba Airport | Cordoba | ES |
| ODC | Oakdale Airport | Oakdale | US |
| ODD | Oodnadatta Airport | Oodnadatta | AU |
| ODE | Beldringe Airport | Odense | DK |
| ODH | Royal Air Force Station | Odiham | GB |
| ODJ | Ouanda Djalle Airport | Ouanda Djalle | CF |
| ODL | Cordillo Downs Airport | Cordillo Downs | AU |
| ODM | Metropolitan Area Airport | Oakland | US |
| ODN | Long Seridan Airport | Long Seridan | MY |
| ODO | Bodaybo Airport | Bodaybo | RU |
| ODR | Ord River Airport | Ord River | AU |
| ODS | Odesa-Central Int'l Airport | Odesa | UA |
| ODW | Oak Harbor Airport | Oak Harbor | US |
| ODY | Oudomxai Airport | Muang Xay | LA |
| OEA | Oneal Airport | Vincennes | US |
| OEC | Oecussi Airport | Oecussi | TL |
| OEL | Yuzhny Airport | Orel | RU |
| OEM | Vincent Fayks Airport | Paloemeu | SR |
| OEO | Osceola Municipal Airport | Osceola | US |
| OER | Ornskoldsvik Airport | Ornskoldsvik | SE |
| OES | San Antonio Oeste Airport | San Antonio Oeste | AR |
| OFF | Off-Line Point | Omaha | US |
| OFI | Ouango Fitini Airport | Ouango Fitini | CI |
| OFJ | Olafsfjordur Airport | Olafsfjordur | IS |
| OFK | Stefan Field | Norfolk | US |
| OFU | Ofu Island Airport | Ofu Island | AS |
| OGA | Searle Field | Ogallala | US |
| OGB | Orangeburg Municipal Airport | Orangeburg | US |
| OGD | Ogden Municipal Airport | Ogden | US |
| OGE | Ogeramnang Airport | Ogeramnang | PG |
| OGG | Kahului Airport | Kahului | US |
| OGL | Ogle Airport | Ogle | GY |
| OGM | Ogobsucum Airport | Ustupu Island | PA |
| OGN | Yonaguni Airport | Yonaguni | JP |
| OGO | Abengourou Airport | Abengourou | CI |
| OGR | Bongor Airport | Bongor | TD |
| OGS | Ogdensburg Airport | Ogdensburg | US |
| OGV | Ongava Airport | Ongava | NA |
| OGX | Ain Beida Airport | Ouargla | DZ |
| OGZ | Beslan Airport | Vladikavkaz | RU |
| OHA | RNZAF Base | Ohakea | NZ |
| OHB | Ambohibary Airport | Moramanga | MG |
| OHC | Northeast Cape Air Force Station | Northeast Cape | US |
| OHD | Ohrid Airport | Ohrid | MK |
| OHE | Gulian Airport | Mohe | CN |
| OHH | Novostroyka Airport | Okha | RU |
| OHI | Oshakati Airport | Oshakati | NA |
| OHO | Okhotsk Airport | Okhotsk | RU |
| OHR | Wyk Airport | Wyk auf Foehr | DE |
| OHT | Kohat Airport | Kohat | PK |
| OIA | Ourilandia Airport | Ourilandia | BR |
| OIC | Eaton Airport | Norwich | US |
| OIL | Splane Memorial Airport | Oil City | US |
| OIM | Oshima Airport | Oshima | JP |
| OIR | Okushiri Airport | Okushiri | JP |
| OIT | Oita Airport | Oita | JP |
| OJC | Johnson Executive Airport | Kansas City | US |
| OKA | Naha Airport | Okinawa | JP |
| OKB | Orchid Beach Airport | Fraser Island | AU |
| OKC | Will Rogers Airport | Oklahoma City | US |
| OKD | Okadama Airport | Sapporo | JP |
| OKE | Okierabu Airport | Okierabu | JP |
| OKF | Okaukuejo Airport | Okaukuejo | NA |
| OKG | Okoyo Airport | Okoyo | CG |
| OKH | Cottesmore RAF | Oakham | GB |
| OKI | Oki Airport | Oki | JP |
| OKJ | Okayama Airport | Okayama | JP |
| OKK | Kokomo Airport | Kokomo | US |
| OKL | Gunung Bintang Airport | Oksibil | ID |
| OKM | Okmulgee Airport | Okmulgee | US |
| OKN | Okondja Airport | Okondja | GA |
| OKO | Yokota AB | Tokyo | JP |
| OKP | Oksapmin Airport | Oksapmin | PG |
| OKQ | Okaba Airport | Okaba | ID |
| OKR | Yorke Island Airport | Yorke Island | AU |
| OKS | Oshkosh Airport | Oshkosh | US |
| OKT | Oktiabrsky Airport | Oktiabrsky | RU |
| OKU | Mokuti Lodge Airport | Mokuti Lodge | NA |
| OKV | Okao Airport | Okao | PG |
| OKY | Army Aviation Centre | Oakey | AU |
| OLA | Orland Airport | Orland | NO |
| OLB | Costa Smeralda Airport | Olbia | IT |
| OLC | Sao Paulo de Olivenca Airport | Sao Paulo de Olivenca | BR |
| OLD | Old Town Airport | Old Town | US |
| OLE | Olean Municipal Airport | Olean | US |
| OLF | Wolf Point International Airport | Wolf Point | US |
| OLH | Old Harbor Sea Plane Base | Old Harbor | US |
| OLI | Rif Airport | Olafsvik | IS |
| OLJ | West Cost Santo Airport | Olpoi | VU |
| OLK | Fuerte Olimpo Airport | Fuerte Olimpo | PY |
| OLL | Ollombo Airport | Oyo | CG |
| OLM | Olympia Airport | Olympia | US |
| OLN | Colonia Sarmiento | Colonia Sarmiento | AR |
| OLO | Neredin Airport | Olomouc | CZ |
| OLP | Olympic Dam Airport | Olympic Dam | AU |
| OLQ | Olsobip Airport | Olsobip | PG |
| OLR | Air Base | Salerno | AF |
| OLS | Nogales International Airport | Nogales | US |
| OLU | Columbus Airport | Columbus | US |
| OLV | Olive Branch Airport | Olive Branch | US |
| OLY | Olney Airport | Olney | US |
| OLZ | Olekminsk Airport | Olekminsk | RU |
| OMA | Eppley Airfield | Omaha | US |
| OMB | Omboue-Hopital Airport | Omboue | GA |
| OMC | Ormoc Airport | Ormoc | PH |
| OMD | Oranjemund Airport | Oranjemund | NA |
| OME | Nome Airport | Nome | US |
| OMF | King Hussein Airport | Mafraq | JO |
| OMG | Omega Airport | Omega | NA |
| OMH | Urumiyeh Airport | Urumiyeh | IR |
| OMI | Omidiyeh Airport | Omidiyeh | IR |
| OMJ | Omura Airport | Nagasaki | JP |
| OMK | Omak Municipal Airport | Omak | US |
| OML | Omkalai Airport | Omkalai | PG |
| OMM | Marmul Airport | Marmul | OM |
| OMO | Mostar International Airport | Mostar | BA |
| OMR | Oradea Airport | Oradea | RO |
| OMS | Tsentralny Airport | Omsk | RU |
| OMY | Preah Vinhear Airport | Thbeng Meanchey | KH |
| ONA | Winona Municipal Airport | Winona | US |
| ONB | Ononge Airport | Ononge | PG |
| OND | Ondangwa Airport | Ondangwa | NA |
| ONE | Onepusu Airport | Onepusu | SB |
| ONG | Mornington Island Airport | Mornington Island | AU |
| ONH | Oneonta Municipal Airport | Oneonta | US |
| ONI | Moanamani Airport | Moanamani | ID |
| ONJ | Odate Noshiro Airport | Odate/Noshiro | JP |
| ONK | Olenek Airport | Olenek | RU |
| ONL | O'Neill Municipal Airport | O'Neill | US |
| ONM | Socorro Airport | Socorro | US |
| ONN | Onion Bay Airport | Onion Bay | US |
| ONO | Ontario Airport | Ontario | US |
| ONP | Newport Airport | Newport | US |
| ONQ | Caycuma Airport | Zonguldak | TR |
| ONR | Monkira Airport | Monkira | AU |
| ONS | Onslow Airport | Onslow | AU |
| ONT | Ontario International Airport | Ontario | US |
| ONU | Ono-i-Lau Airport | Ono-i-Lau | FJ |
| ONX | Colon Airport | Colon | PA |
| ONY | Olney Airport | Olney | US |
| OOA | Oskaloosa Municipal Airport | Oskaloosa | US |
| OOK | Toksook Bay Airport | Toksook Bay | US |
| OOL | Coolangatta Airport | Gold Coast | AU |
| OOM | Snowy Mountains Airport | Cooma | AU |
| OOR | Mooraberree Airport | Mooraberree | AU |
| OOT | Onotoa Airport | Onotoa | KI |
| OPA | Kopasker Airport | Kopasker | IS |
| OPB | Open Bay Airport | Open Bay | PG |
| OPF | Opa Locka | Miami | US |
| OPI | Oenpelli Airport | Oenpelli | AU |
| OPL | St Landry Parish Airport | Opelousas | US |
| OPO | Porto Airport | Porto | PT |
| OPS | Sinop Airport | Sinop | BR |
| OPU | Balimo Airport | Balimo | PG |
| OPW | Opuwo Airport | Opuwo | NA |
| ORA | Oran Airport | Oran | AR |
| ORB | Orebro-Bofors Airport | Orebro | SE |
| ORC | Orocue Airport | Orocue | CO |
| ORD | O'Hare International Airport | Chicago | US |
| ORE | St . Denis de l'Hotel | Orleans | FR |
| ORF | Norfolk International Airport | Norfolk | US |
| ORG | Zorg En Hoop Airport | Paramaribo | SR |
| ORH | Worcester Airport | Worcester | US |
| ORI | Port Lions Sea Plane Base | Port Lions | US |
| ORJ | Orinduik Airport | Orinduik | GY |
| ORK | Cork International Airport | Cork | IE |
| ORL | Herndon Airport | Orlando | US |
| ORM | Sywell Airport | Northampton | GB |
| ORN | Es Senia Airport | Oran | DZ |
| ORO | Yoro Airport | Yoro | HN |
| ORP | Orapa Airport | Orapa | BW |
| ORQ | Norwalk Heliport | Norwalk | US |
| ORR | Yorktown Airport | Yorktown | AU |
| ORS | Waterport SPB | Orpheus Island | AU |
| ORT | Northway Airport | Northway | US |
| ORU | Oruro Airport | Oruro | BO |
| ORV | Curtis Memorial Airport | Noorvik | US |
| ORW | Ormara Airport | Ormara | PK |
| ORX | Oriximina Airport | Oriximina | BR |
| ORY | Orly Field | Paris | FR |
| ORZ | Orange Walk Airport | Orange Walk | BZ |
| OSA | Metropolitan Area | Osaka | JP |
| OSB | Osage Beach Airport | Osage Beach | US |
| OSC | Wurtsmith Air Force Base | Oscoda | US |
| OSD | Froesoe Airport | Ostersund | SE |
| OSE | Omora Airport | Omora | PG |
| OSF | Ostafyevo Airport | Podolsk | RU |
| OSG | Ossima Airport | Ossima | PG |
| OSH | Wittman Field | Oshkosh | US |
| OSI | Osijek Airport | Osijek | HR |
| OSK | Oskarshamn Airport | Oskarshamn | SE |
| OSL | Oslo Airport | Oslo | NO |
| OSM | Mosul International Airport | Mosul | IQ |
| OSN | Air Base | Osan | KR |
| OSO | Osborne Mine Airport | Osborne Mine | AU |
| OSR | Leos Janacek Airport | Ostrava | CZ |
| OSS | Osh Airport | Osh | KG |
| OST | Oostende/Brugge Airport | Oostende/Brugge | BE |
| OSU | Ohio State University Airport | Columbus | US |
| OSW | Orsk Airport | Orsk | RU |
| OSX | Attala County Airport | Kosciusko | US |
| OSY | Namsos Airport | Namsos | NO |
| OSZ | Zegrze Pomorskie AB | Koszalin | PL |
| OTA | Mota Airport | Mota | ET |
| OTC | Berim Airport | Bol | TD |
| OTD | Contadora Airport | Contadora | PA |
| OTG | Worthington Airport | Worthington | US |
| OTH | North Bend Airport | North Bend | US |
| OTI | Pitu Airport | Morotai Island | ID |
| OTJ | Otjiwarongo Airport | Otjiwarongo | NA |
| OTK | Tillamook Airport | Tillamook | US |
| OTL | Boutilimit Airport | Boutilimit | MR |
| OTM | Industrial Airport | Ottumwa | US |
| OTN | Green Airport | Oaktown | US |
| OTO | Vor Airport | Otto | US |
| OTP | Otopeni International Airport | Bucharest | RO |
| OTR | Coto 47 Airport | Coto 47 | CR |
| OTS | Anacortes Airport | Anacortes | US |
| OTT | Andre Maggi Airport | Cotriguacu | BR |
| OTU | Otu Airport | Otu | CO |
| OTV | Ontong Java Atoll Airport | Ontong Java Atoll | SB |
| OTY | Oria Airport | Oria | PG |
| OTZ | Kotzebue Airport | Kotzebue | US |
| OUA | Ouagadougou Airport | Ouagadougou | BF |
| OUD | Angads Airport | Oujda | MA |
| OUE | Ouesso Airport | Ouesso | CG |
| OUG | Ouahigouya Airport | Ouahigouya | BF |
| OUH | Oudtshoorn Airport | Oudtshoorn | ZA |
| OUK | Outer Skerries Airport | Out Skerries | GB |
| OUL | Oulu Airport | Oulu | FI |
| OUM | Oum Hadjer Airport | Oum Hadjer | TD |
| OUN | Max Westheimer Airport | Norman | US |
| OUQ | Railway Station | Ourense | ES |
| OUR | Batouri Airport | Batouri | CM |
| OUS | Ourinhos Airport | Ourinhos | BR |
| OUT | Bousso Airport | Bousso | TD |
| OUU | Ouanga Airport | Ouanga | GA |
| OUZ | Tazadit Airport | Zouerate | MR |
| OVA | Bekily Airport | Bekily | MG |
| OVB | Tolmachevo Airport | Novosibirsk | RU |
| OVD | Asturias Airport | Asturias | ES |
| OVE | Oroville Airport | Oroville | US |
| OVG | AFB | Overberg | ZA |
| OVI | Railway Station | Oviedo | ES |
| OVL | Ovalle Airport | Ovalle | CL |
| OVR | Olavarria Airport | Olavarria | AR |
| OVS | Sovetsky Airport | Sovetsky | RU |
| OWA | Owatonna Airport | Owatonna | US |
| OWB | Daviess County Airport | Owensboro | US |
| OWD | Norwood Memorial Airport | Norwood | US |
| OWE | Owendo Airport | Owendo | GA |
| OWK | Central Maine Airport | Norridgewock | US |
| OXB | Osvaldo Vieira International Airport | Bissau | GW |
| OXC | Waterbury-Oxford Airport | Oxford | US |
| OXD | Miami University Airport | Oxford | US |
| OXF | London Oxford Airport | Oxford | GB |
| OXO | Orientos Airport | Orientos | AU |
| OXR | Oxnard Airport | Oxnard | US |
| OXY | Morney Airport | Morney | AU |
| OYA | Goya Airport | Goya | AR |
| OYE | Oyem Airport | Oyem | GA |
| OYG | Moyo Airport | Moyo | UG |
| OYK | Oiapoque Airport | Oiapoque | BR |
| OYL | Moyale Airport | Moyale | KE |
| OYN | Ouyen Airport | Ouyen | AU |
| OYO | Tres Arroyos Airport | Tres Arroyos | AR |
| OYP | St-Georges de lOyapock | St Georges de lOyapock | GF |
| OYS | Yosemite National Park Airport | Yosemite National Park | US |
| OZA | Ozona Airport | Ozona | US |
| OZC | Labo Airport | Ozamis | PH |
| OZG | Zagora Airport | Zagora | MA |
| OZH | Mokraya International Airport | Zaporizhzhia | UA |
| OZI | Railway Station | Bobadilla | ES |
| OZL | Ferry Port | Orzola | ES |
| OZP | Air Base | Moron | ES |
| OZR | Cairns Army Air Field | Ozark | US |
| OZU | Railway Station | Montilla | ES |
| OZZ | Ouarzazate Airport | Ouarzazate | MA |