| City/Airport Name | Country | Airport Code | |
| OAKLAND INTERNATIONAL | USA | KOAK | USA (CALIFORNIA) |
| OAMARU | New Zealand | NZOU | |
| OAXACA | Mexico | MMOX | |
| OBERPFAFFENHOFEN | Germany | EDMO | |
| OBIHIRO | Japan | RJCB | |
| OBO M'BOKI | | FEFB | CENTRAL AFRICAN REP. |
| OCANA | Colombia | SKOC | |
| OCHO RIOS BOSCOBEL | Jamaica | MKBS | |
| ODENSE BELDRINGE | Denmark | EKOD | |
| ODESSA TSNTRALNY | Ukraine | UKOO | |
| ODIENNE | Ivory Coast | DIOD | |
| OGDENSBURG | USA | KOGS | USA (NEW YORK) |
| OHRID | Macedonia | LWOH | FORMER MACEDONIA |
| OITA | Japan | RJFO | |
| OKABA | Indonesia | WAKO | |
| OKAUKUEJO | Namibia | FAOO | |
| OKAYAMA | Japan | RJOB | |
| OKI ISLAND | Japan | RJNO | |
| OKLAHOMA CITY WILL ROGER WORLD | USA | KOKC | USA (OKLAHOMA) |
| OKONDJA | Gabon | FOGQ | |
| OKSIBIL | Indonesia | WAJO | |
| OKUSHIRI | Japan | RJEO | |
| OLBIA COSTA SMERALDA | Italy | LIEO | |
| OLD CROW | Canada | CYOC | CANADA (YT) |
| OMAHA EPPLEY AIRFIELD | USA | KOMA | |
| OMBOUE HOSPIAL | Gabon | FOOH | |
| OMSK | Russia | UNOO | |
| ONDANGWA | Namibia | FAOA | |
| ONOTOA | Kiribati | NGON | |
| ONTARIO INTERNATIONAL | USA | KONT | USA (CALIFORNIA) |
| ORADEA | Romania | LROD | |
| ORAN ES SENIA | Algeria | DAOO | |
| ORANJEMUND | Namibia | FAOG | |
| ORAPA | Botswana | FBOR | |
| OREBRO | Sweden | ESOE | |
| ORENBURG CENTRAL | Russia | UWOO | |
| ORLANDO INTERNATIONAL | USA | KORL | USA (FLORIDA) |
| ORMARA MIL. & CIVIL | Pakistan | OPOR | |
| ORNSKOLDSVIK | Sweden | ESNO | |
| ORSTA-VOLDA HOVDEN | Norway | ENOV | |
| OSAKA INTERNATIONAL | Japan | RJOO | |
| OSAKA KANSAI INTERNATIONAL | Japan | RJBB | |
| OSH | Russia | UAFO | |
| OSHAKATI | Namibia | FAOS | |
| OSHIMA | Japan | RJTO | |
| OSKARSHAMN | Sweden | ESMO | |
| OSLO FORNEBU | Norway | ENFB | |
| OSLO GARDERMOEN | Norway | ENGM | |
| OSORNO CANAL BAJO HOTT | Chile | SCJO | |
| OSTEND | Belgium | EBOS | |
| OSTERSUND FROSON | Sweden | ESPC | |
| OTTAWA UPLANDS INTERNATIONAL | Canada | CYOW | CANADA (ONTARIO) |
| OTU OTU | Colombia | SKOT | |
| OUAGADOUGOU INTERNATIONAL | Burkina Faso | DFFD | |
| OUAHIGOUYA | Burkina Faso | DFCC | |
| OUANGO FITINI | Ivory Coast | DIOF | |
| OUARGLA | Algeria | DAUU | |
| OUARZAZATE | Morocco | GMMZ | |
| OUDOMXAY | Laos | VLOS | |
| OUESSO | Congo, Democratic Republic of | FCOU | CONGO |
| OUJDA ANGADS | Morocco | GMFO | |
| OULU | Finland | EFOU | |
| OURINHOS | Brazil | SBOU | BRAZIL (SP) |
| OUVEA OULOUP | New Caledonia | NWWV | NEW CALEDONIA (F) |
| OVDA OVDA | Israel | LLOV | |
| OWANDO | Congo, Democratic Republic of | FCOO | CONGO |
| OYEM | Gabon | FOGO | |
