World Sea Ports
| Port Name | Port Code | Country Name |
|---|---|---|
| Östrand | SEOST | Sweden |
| Ostseebad Goehren | DEOGO | Germany |
| Ostseebad Kuhlungsborn | DEOKG | Germany |
| Osuki | JPOSU | Japan |
| Oswaldtwistle | GBOWW | United Kingdom |
| Oswego | USOSW | United States of America (the) |
| Ota | FRPO4 | France |
| Otago Harbour | NZORR | New Zealand |
| Otake | JPOTK | Japan |
| Otao | JPOTA | Japan |