| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Oana | WAH-nah | Romanian | ||
| Obdulia | - | Spanish | ||
| Obi | - | Western African, Igbo | ||
| Obrad | - | Serbian | ||
| Ochieng | - | Eastern African, Luo | ||
| Octavia | ahk-TAYV-ee-ə (English) | English, Spanish, Ancient Roman | ||
| Octavian | ahk-TAYV-ee-ən (English) | History, Romanian | ||
| Octavianus | - | Ancient Roman | ||
| Octavio | ok-TAH-vyo | Spanish | ||
| Octavius | ahk-TAYV-ee-əs (English) | Ancient Roman | ||
| Oda | O-dah (German) | German, Ancient Germanic | ||
| Odalis | - | Spanish | ||
| Odalric | - | Ancient Germanic | ||
| Odalys | - | Spanish | ||
| Odarka | - | Ukrainian |