| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Orsino | - | Italian | ||
| Orso | - | Italian | ||
| Orsola | OR-so-lah | Italian | ||
| Osanna | - | Italian (Rare) | ||
| Oscar | AHS-kər (English) | English, Irish, Portuguese (Brazilian), Italian, Swedish, Norwegian, Danish, Dutch, French, Irish My | ||
| Osvaldo | - | Spanish, Italian, Portuguese | ||
| Ottavia | - | Italian | ||
| Ottaviano | - | Italian | ||
| Ottavio | - | Italian | ||
| Ottone | - | Italian | ||
| Ottorino | - | Italian | ||
| Ovidio | - | Italian, Spanish |