| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| OĽGa | - | Slovak | ||
| OŽBalt | - | Slovene | ||
| OŽBej | - | Slovene | ||
| Obdulia | - | Spanish | ||
| Obi | - | Western African, Igbo | ||
| Obrad | - | Serbian | ||
| Ocean | O-shən | English (Rare) | ||
| Ochieng | - | Eastern African, Luo | ||
| OctÁVia | - | Portuguese | ||
| OctÁVio | - | Portuguese | ||
| Octavia | ahk-TAYV-ee-ə (English) | English, Spanish, Ancient Roman | ||
| Octavian | ahk-TAYV-ee-ən (English) | History, Romanian | ||
| Octavio | ok-TAH-vyo | Spanish | ||
| Odalis | - | Spanish | ||
| Odalys | - | Spanish |