- Openheart's Society -- Opera Ebony
- Opera Familia -- Opera Theatre Of Rochester Chorus
- Opera Theatre of St Louis & St Louis Symphony Orch -- Operation Beast Mode
- Operation Big Shots -- Operations Big Shots
- Operator -- Opgave
- Opgeduveld -- Ophelia's Dream
- Ophelia's Dream -- Ophélie Winter
- Ophlux -- Opie's Dream
- Opihi Pickers -- Opium Rose
- Opium Taylor -- Opossum Gang
- Opossum Holler -- Opposite Exhale
- Opposite Pole -- Oprica Ivancea
- Oprlid -- Optical
- Optical Blue -- Optimist Prime
- Optimistic -- Optina Pustyn Male Choir
- Optina Pustyn Male Choir -- Opus
- Opus 1 -- Opus Bridge
- Opus Crobag -- Opus Posthumous/Pokrovsky...
- Opus Quatro -- Or & 2nd Reality
- or-if-is -- Oracle 9000
- Oracle King -- Oran Etkin
- Oran G -- Orange
- Orange -- Orange Brothers
- Orange Bud -- Orange Factory