| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Obdulia | - | Spanish | ||
| Octavia | ahk-TAYV-ee-ə (English) | English, Spanish, Ancient Roman | ||
| Octavio | ok-TAH-vyo | Spanish | ||
| Odalis | - | Spanish | ||
| Odalys | - | Spanish | ||
| Ofelia | o-FE-lyah | Spanish, Italian | ||
| Olalla | o-LAH-yah | Spanish | ||
| Olegario | - | Spanish | ||
| 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 | ||
| Orfeo | - | Italian, Spanish | ||
| Osvaldo | - | Spanish, Italian, Portuguese | ||
| Ovidio | - | Italian, Spanish |