• Oberlin Consort of Viols
• OGMA
• Olexa Kabanov
• Oliostere
• One Sock Thief
• Opened Paradise
• Opera Rock
• Optimal Tunes
• Orinda
• Osamu Kitajima and Chris Mancinelli
• Ostracon
• OTiS
• Ou
• Ozzie Cruse