| Osama | | - | Arabic | |
| Osanne | | - | French (Rare) | |
| Oscar | | AHS-kər (English) | English, Irish, Portuguese (Brazilian), Italian, Swedish, Norwegian, Danish, Dutch, French, Irish My | |
| Osee | | - | Biblical Latin, Biblical Greek | |
| Oshea | | - | Biblical | |
| Otakar | | - | Czech | |
| Othmar | | - | German, Czech, Ancient Germanic | |
| Othniel | | AWTH-nee-əl (English) | Biblical | |
| Otho | | - | Ancient Roman | |
| Otieno | | - | Eastern African, Luo | |
| Otmar | | - | German, Ancient Germanic | |
| Otokar | | - | Czech | |
| OttÓ | | - | Hungarian, Icelandic | |
| Otto | | AW-to (German), AH-to (English), OT-to (Finnish) | German, Swedish, Norwegian, Danish, Dutch, English, Finnish, Ancient Germanic | |
| Ourbanos | | - | Biblical Greek | |