| Oleksander | | - | Ukrainian | |
| Oleksandr | | - | Ukrainian | |
| Oleksandra | | - | Ukrainian | |
| Oleksiy | | - | Ukrainian | |
| Olena | | - | Ukrainian | |
| Oles | | - | Ukrainian | |
| Olev | | - | Estonian | |
| Olexiy | | - | Ukrainian | |
| Olga | | OL-gah (Russian), AWL-gah (Polish, German) | Russian, Ukrainian, Polish, German, Swedish, Norwegian, Danish, Icelandic, Latvian, Hungarian, Itali | |
| Olgica | | - | Macedonian, Serbian | |
| Olha | | - | Ukrainian | |
| Olimpia | | aw-LEEM-pyah (Polish) | Italian, Spanish, Romanian, Polish, Hungarian | |
| OlivÉR | | O-lee-vayr | Hungarian | |
| Oliva | | - | Late Roman | |
| Oliver | | AHL-ə-vər (English), AW-lee-ver (German), O-lee-ver (Finnish) | English, German, Swedish, Norwegian, Danish, Finnish, Estonian, Serbian, Croatian, Macedonian, Czech | |