| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Othmar | - | German, Czech, Ancient Germanic | ||
| Otho | - | Ancient Roman | ||
| Otis | O-tis | English | ||
| Otmar | - | German, Ancient Germanic | ||
| Otto | AW-to (German), AH-to (English), OT-to (Finnish) | German, Swedish, Norwegian, Danish, Dutch, English, Finnish, Ancient Germanic | ||
| Ottoline | - | English (Rare) | ||
| Ovidius | - | Ancient Roman | ||
| Owen (1) | O-ən (English) | Welsh, English | ||
| Oz (1) | AHZ | English | ||
| Ozzie | AHZ-ee | English | ||
| Ozzy | AHZ-ee | English |