This article features a list of islands sorted by their name beginning with the letter O.
{{dynamic list}}{{A-Z multipage list|format=()|List of islands by name}}| Island’s Name | Island group(s) | Country/Countries | |
| Oahu | Hawaii}} | United States}} |
| Oak | Ontario}} | Canada}} |
| Óbudai-sziget | Danube River | Hungary}} |
| Obstruction | Washington}} | United States}} |
| Oconnel | Iowa}} | United States}} |
| Ocracoke | North Carolina}} | United States}} |
| Oeno | Pitcairn Islands}} | United Kingdom}} British overseas territories |
| Ofidoussa |
| Ogami | Miyako Islands part of the Sakishima Islands part of the Ryukyu Islands | Japan}} |
| Oinousses | Greece}} |
| Oki daitō | Daitō Islands part of the Ryukyu Islands | Japan}} |
| Okikendawt | Ontario}} | Canada}} |
| Okinawa | Okinawa Islands part of the Ryukyu Islands | Japan}} |
| Okinoerabujima | Amami Islands part of the Satsunan Islands part of the Ryukyu Islands | Japan}} |
| Oland | North Frisian Islands | Germany}} |
| Öland | Sweden}} |
| Oleron | France}} |
| Olib | Northern Dalmatia | Croatia}} |
| Ombo | Ryfylke Islands, Rogaland | Norway}} |
| Omelek | Kwajalein Atoll, Ralik Chain | Marshall Islands}} |
| Omø | Great Belt | Denmark}} |
| Omolkarm | Persian Gulf | Iran}} |
| Ono | Alabama}} | United States}} |
| Ontong Java | Solomon Islands | Solomon Islands}} |
| Orcas | Washington}} | United States}} |
| Öreg-sziget | Danube River | Hungary}} |
| Orfasay | Shetland Islands}} | Scotland}} |
| Oronsay | Inner Hebrides | Scotland}} |
| Orust | Sweden}} |
| Izu Ōshima | Izu Islands | Japan}} |
| Osmussaar | Gulf of Finland | Estonia}} |
| Ostrów | Islands of Gdańsk | Poland}} |
| Othonoi | Ionian Islands | Greece}} |
| Otok | Bay of Kotor Islands | Montenegro}} |
| Out Stack | Shetland Islands}} | Scotland}} |
| Outer Duck | Ontario}} | Canada}} |
| Ovau | Shortland Islands | Solomon Islands}} |
| Ovoa | Beira Litoral Islands | Portugal}} |
| Oxeia | Ionian Islands | Greece}} |
| Oxna | Shetland Islands}} | Scotland}} |
| Owens | Kentucky}} | United States}} |
| Owl | Ireland}} |
| Oyster Rock | Maharashtra | India}} |