| Oddo | | - | Italian | |
| Ofelia | | o-FE-lyah | Spanish, Italian | |
| Olga | | OL-gah (Russian), AWL-gah (Polish, German) | Russian, Ukrainian, Polish, German, Swedish, Norwegian, Danish, Icelandic, Latvian, Hungarian, Itali | |
| 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 | |