| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Omiros | - | Greek | ||
| Onesimos | - | Ancient Greek, Biblical Greek | ||
| Onesiphoros | - | Ancient Greek, Biblical Greek | ||
| Orestes | o-RES-teez (English) | Greek Mythology | ||
| Origenes | - | Ancient Greek | ||
| Orion | o-RIE-ən (English) | Greek Mythology | ||
| Orpheus | AWR-fee-əs (English) | Greek Mythology | ||
| Osee | - | Biblical Latin, Biblical Greek | ||
| Ourania | - | Greek Mythology | ||
| Ouranos | - | Greek Mythology | ||
| Ourbanos | - | Biblical Greek | ||
| Ouri | - | Biblical Greek | ||
| Ourias | - | Biblical Greek | ||
| Ozazias | - | Biblical Greek | ||
| Ozi | - | Biblical Latin, Biblical Greek |