Historical typefaces (like poluustav (semi-uncial), a standard font style for the Church Slavonic typography) and old manuscripts represent several additional glyph variants of Cyrillic O, both for decorative and orthographic (sometimes also "hieroglyphic"[1]) purposes, namely: In Russian, O is used word-initially, after another vowel, and after non-palatalized consonants.

Because of a vowel reduction processes, the Russian /o/ phoneme may have a number of pronunciations in unstressed syllables, including [ɐ] and [ə].

In Macedonian, Bulgarian, Ukrainian and Belarusian, the letter represents the sound /ɔ/.

In Tuvan the Cyrillic letter can be written as a double vowel.

[4] Exotic glyph variants of Cyrillic O are available only in Unicode:[5][6][7][8][9]