| O’neill | O’Shea | Ó?inn |
| O?ulcan | O?uzhan | Oane |
| Obaid | Obaida | Obayd |
| Obbe | Obeed | Obell |
| Ocker | Octavian | Octavius |
| Oday | Oden | Odin |
| Odoin | Odysseas | Oebaida |
| Oebele | Oeds | Oedse |
| Oek | Oene | Oesama |
| Oetze | Oger | Oggi |
| Ogulcan | Oguz | Oguzhan |
| Ogün | Ois?n | Oisin |
| Ojani | Okan | Okke |
| Okke-Bas | Oktawian | Oktay |
| Okyanus | Olademeji | Olaf |
| Olaf-Kári | Olamide | Olan |
| Olander | Olatokunbo | Olav |
| Olawale | Olayinka | Ole |
| Ole-Mads | Olef | Olek |
| Olger | Olin | Olín |
| Oliver | Olivier | Olivier-Laurens |
| Oliwier | Olke | Olle |
| Olli | Ollie | Olliver |
| Olof | Oltian | Oluwaseyi |
| Oluwasolabomi | Olver | Omar |
| Omari | Omarion | Omed |
| Omeed | Omer | Omesh |
| Omid | Omied | Omran |
| Omri | One | Onesime |
| Onne | Onno | Onur |
| Onurcan | Onyedikachi | Onyeka |
| Oole | Oras | Oraz |
| Orçun | Ordwin | Orestis |
| Orfeas | Orgelsio | Orhan |
| Orhun | Orion | Orjaydiyo |
| Orkas | Orlando | Orlin |
| Orly | Orsen | Orso |
| Orson | Orville | Osahenrhunmwen |
| Osahenrumwen | Osama | Osazee |
| Oscar | Osewanhu | Osher |
| Osias | Osinachi | Osiris |
| Oskar | Osmaan | Osman |
| Ostin | Osumane | Ot |
| Otcar | Othman | Othniël |
| Otilio | Otis | Otman |
| Otso | Otte | Otto |
| Ouadie | Ouail | Ouaïl |
| Ouaïss | Ouakil | Oualid |
| Ouasim | Ouassil | Ouassim |
| Oubaid | Oubayd | Ouissam |
| Oumair | Oumar | Ousama |
| Ousayd | Ousman | Ousmane |
| Oussama | Outmane | Ouwie |
| Ove | Owais | Owan |
| Owen | Owin | Oyke |
| Oytun | Ozan |