| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Omolara | - | Western African, Yoruba | ||
| Ondina | - | Portuguese, Italian | ||
| Oni | - | Western African, Yoruba | ||
| Onyeka | - | Western African, Igbo | ||
| Onyekachi | - | Western African, Igbo | ||
| Onyekachukwu | - | Western African, Igbo | ||
| Opeyemi | - | Western African, Yoruba | ||
| Orabela | o-rah-BE-lah | Esperanto | ||
| Osamu | o-sah-moo | Japanese | ||
| Oscar | AHS-kər (English) | English, Irish, Portuguese (Brazilian), Italian, Swedish, Norwegian, Danish, Dutch, French, Irish My | ||
| Osvaldo | - | Spanish, Italian, Portuguese | ||
| OtÁVia | - | Portuguese (Brazilian) | ||
| OtÁVio | - | Portuguese (Brazilian) | ||
| OvÍDio | - | Portuguese | ||
| Oyibo | - | Western African, Urhobo |