| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Oceanus | - | Greek Mythology (Latinized) | ||
| Odysseus | o-DIS-ee-əs (English) | Greek Mythology | ||
| Oedipus | ED-i-pəs (English), EED-i-pəs (English) | Greek Mythology (Latinized) | ||
| Oenone | - | Greek Mythology (Latinized) | ||
| Oidipous | - | Greek Mythology | ||
| Oinone | - | Greek Mythology | ||
| Okeanos | - | Greek Mythology | ||
| Orestes | o-RES-teez (English) | Greek Mythology | ||
| Orion | o-RIE-ən (English) | Greek Mythology | ||
| Orpheus | AWR-fee-əs (English) | Greek Mythology | ||
| Ourania | - | Greek Mythology | ||
| Ouranos | - | Greek Mythology |