| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Odessa | - | Various | ||
| Oksana | ahk-SAH-nah (Russian) | Ukrainian, Russian | ||
| Oleg | ah-LYEK | Russian | ||
| Olga | OL-gah (Russian), AWL-gah (Polish, German) | Russian, Ukrainian, Polish, German, Swedish, Norwegian, Danish, Icelandic, Latvian, Hungarian, Itali | ||
| Olya | - | Russian | ||
| Omega | o-MAY-gə (English) | Various | ||
| Onisim | - | Russian (Rare) | ||
| Oprah | O-prə (English) | Various | ||
| Osip | O-seep | Russian | ||
| Ouida | - | Various | ||
| Oxana | - | Ukrainian, Russian |