| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Oddo | - | Italian | ||
| Ofelia | o-FE-lyah | Spanish, Italian | ||
| Olimpia | aw-LEEM-pyah (Polish) | Italian, Spanish, Romanian, Polish, Hungarian | ||
| Olivia | ə-LIV-ee-ə (English), o-LEE-vyah (Italian, Spanish), o-LEE-vee-ah (German), O-lee-vee-ah (Finnish) | English, Italian, Spanish, German, Finnish, Swedish, Norwegian, Danish | ||
| Oliviero | o-lee-VYE-ro | Italian | ||
| Ondina | - | Portuguese, Italian | ||
| Orazio | - | Italian | ||
| Orfeo | - | Italian, Spanish | ||
| Oria | - | Italian | ||
| Oriana | o-RYAH-nah | Italian | ||
| Orlanda | or-LAHN-dah | Italian | ||
| Orlando | or-LAHN-do | Italian | ||
| Ornella | - | Italian | ||
| Orsina | - | Italian | ||
| Orsino | - | Italian |