| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 1921 | Ophelia | Greek | Help. Serpentine. In Shakespeare's 'Hamlet', Ophelia was the lover of Hamlet who went insane as a result of his irrational behavior. | F | |
| 1922 | Ophelie | Greek | Wisdom. | F | |
| 1923 | Ophion | Greek | A serpent. | M | |
| 1924 | Orea | Greek | From the mountain. | F | |
| 1925 | Oreias | Greek | From the mountain. | M | |
| 1926 | Oreste | Greek | From the mountain. | M | |
| 1927 | Orestes | Greek | From the mountain. | M | |
| 1928 | Oria | Greek | From the mountain. | F | |
| 1929 | Orion | Greek | Rising in the sky; dawning. Mythological Orion was a mighty hunter and son of Poseidon. The constellation Orion contains three conspicuous stars. | M | |
| 1930 | Orpheus | Greek | Son of Apollo. | M | |
| 1931 | Orthros | Greek | Guardian of Geryon. | M | |
| 1932 | Ortygia | Greek | Calypso's island. | F | |
| 1933 | Otis | Greek | Keen of hearing. | M | |
| 1934 | Otos | Greek | Keen of hearing. | M | |
| 1935 | Otus | Greek | Keen of hearing. | M | |
| 1936 | Owain | Greek | Variant of Eugene: Well-born. Famous bearer: Prince Eugene of Savoy; American playwright Eugene O'Neill. | M | |
| 1937 | Owen | Greek | Variant of Eugene: Well-born. Famous bearer: Prince Eugene of Savoy. | M | |
| 1938 | Page | Greek | Child. | F | |
| 1939 | Palaemon | Greek | A sea god. | M | |
| 1940 | Palamedes | Greek | Son of Nauplius. | M | |