| Obdulia | | - | Spanish | |
| Obed | | O-bed (English) | Biblical, Biblical Latin, Biblical Greek | |
| Oberon | | O-bər-ahn (English) | Literature | |
| Obi | | - | Western African, Igbo | |
| Obrad | | - | Serbian | |
| Ocean | | O-shən | English (Rare) | |
| Oceanus | | - | Greek Mythology (Latinized) | |
| 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 | |