| Oswulf | Man | English Names |
| Oteria | Woman | German - Old High German Names |
| Othello | Man | Italian Names |
| Othmar | Man | German Names |
| Othniel | Man | Hebrew Names |
| Otieno | Man | African - Kenya Names |
| Otis | Man | English Names |
| Otón | Man | Spanish Names |
| Otso | Man | Scandinavian - Finnish Names |
| Ottavia | Woman | Italian Names |
| Ottelien | Woman | Dutch Names |
| Ottilia | Woman | Scandinavian Names |
| Ottilie | Woman | German Names |
| Otto | Man | German Names |
| Ottoline | Woman | French Names |
| Ottorino | Man | Italian Names |
| Otylia | Woman | Polish Names |
| Ouida | Woman | French Names |
| Ourania | Woman | Greek Names |
| Ouray | Unisex | Native American - Ute Names |