| Ocean | | O-shən | English (Rare) | |
| Octavia | | ahk-TAYV-ee-ə (English) | English, Spanish, Ancient Roman | |
| Ode | | - | Medieval English | |
| Odelia | | - | English | |
| Odell | | o-DEL | English | |
| Odetta | | - | English (Rare) | |
| Odin | | O-din | Norse Mythology, English (Modern) | |
| Ogden | | AWG-dən | English | |
| Oli | | AHL-ee | English | |
| Olive | | AHL-iv | English | |
| 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 | |
| Ollie | | AHL-ee | English | |
| Olyvia | | ə-LIV-ee-ə | English (Rare) | |
| Omar (1) | | - | Arabic, English | |