Cognomen Oii (Oii 
) , in all the world, is quite a rare last name. The last name Oii is habitual in Papua New Guinea, where it is quite a rare surname, Malaysia, and Singapore, where it is a rare surname. Measured by absolute frequency, the name is most common in Indonesia, Malaysia, and Papua New Guinea. Much less frequently, Oii is the forename as well as the last name.