| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Onur | - | Turkish | ||
| Onyeka | - | Western African, Igbo | ||
| Onyekachi | - | Western African, Igbo | ||
| Onyekachukwu | - | Western African, Igbo | ||
| Oona | OO-na (Irish), O:-nah (Finnish) | Irish, Finnish | ||
| Oonagh | OO-na | Irish | ||
| Opal | O-pəl | English | ||
| Opaline | O-pə-leen | English (Rare) | ||
| Opeyemi | - | Western African, Yoruba | ||
| Ophelia | o-FEEL-yə (English) | English, Literature | ||
| Ophiuchus | - | Astronomy | ||
| Oprah | O-prə (English) | Various | ||
| Ora (1) | - | English | ||
| Orabela | o-rah-BE-lah | Esperanto | ||
| Oral | - | English (Rare) |