These names are from a list of 6000 names given to Finnish children (aged 1 to 10 years old). Some of the names may seem ordinary to Anglophones, but in Finland they're still considered rare and/or unique.
Obelix
ObiObike
Obomate
OdinOhtli
Ohto
Oki
Okkar
Okke
Okki
Okko
Okko-Alvar
Okko-Severi
OlaOlavi-Jako
OleOleksandrOleksi
Oliwer
Oliver-Jako
Olivers
OlleOlli-Elias
Olli-Jussi
Olli-Pekka
Olmo
OlofOmarOmerOmidOnni-Eemeli
Onni-Eemil
Onni-Eetu
Onnikalle
Onnimanni
Onni-Martti
Onni-Matias
Onni-Matti
Onni-Mikael
Onni-Noa
Onni-Oskari
Onni-Pekka
Onni-Poika
Onni-Sameli
Onni-Valtteri
Oras - means "sprout" in Finnish
OscarOscari
Oska
OskuOsmanOssianOtava - Big Dipper's or Plough's (the asterism) Finnish name; "otava" is an old Finnish word for a salmon net
Otto-Akusti
Otto-Elias
Otto-Kalle
Otto-Pavel
Otto-Pekka
Otto-Ville
Oula
Ousmane
Outa