| Obe | Obi | Ocean |
| Océan | Octave | Odiel |
| Odin | Oguz | Oguzhan |
| Oisin | Okan | Olaf |
| Ole | Oliver | Olivier |
| Oliwier | Olsen | Omar |
| Omer | Onno | Onur |
| Opoku | Orazio | Orçun |
| Orhan | Orion | Orlando |
| Orvil | Oscar | Oskar |
| Osman | Ossama | Ossian |
| Othman | Othmane | Otis |
| Otman | Otto | Otto-Jan |
| Ouail | Oualid | Ouassim |
| Oumar | Oumarou | Ousmane |
| Oussama | Owen | Ozan |
| Ozias |