| Olaf | | O-lahf (German, Dutch) | Norwegian, Danish, German, Dutch, Polish | |
| Olav | | - | Norwegian, Danish | |
| Ole | | OL-e (Danish) | Danish, Norwegian | |
| Olga | | OL-gah (Russian), AWL-gah (Polish, German) | Russian, Ukrainian, Polish, German, Swedish, Norwegian, Danish, Icelandic, Latvian, Hungarian, Itali | |
| Oliver | | AHL-ə-vər (English), AW-lee-ver (German), O-lee-ver (Finnish) | English, German, Swedish, Norwegian, Danish, Finnish, Estonian, Serbian, Croatian, Macedonian, Czech | |
| 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 | |
| Oluf | | - | Danish | |
| Orla (2) | | - | Danish | |
| Oscar | | AHS-kər (English) | English, Irish, Portuguese (Brazilian), Italian, Swedish, Norwegian, Danish, Dutch, French, Irish My | |
| Oskar | | AWS-kahr (German, Polish) | Swedish, Norwegian, Danish, German, Polish | |
| Osvald | | - | Swedish, Norwegian, Danish | |
| Otto | | AW-to (German), AH-to (English), OT-to (Finnish) | German, Swedish, Norwegian, Danish, Dutch, English, Finnish, Ancient Germanic | |
| Ove | | - | Swedish, Norwegian, Danish | |