O.a.r. (of A Revolution) Oasis Oathean Obituary Obliveon Obsidian Gate Obtest Occult Ocean Colour Scene Offertorium Office Officium Triste Ofra Haza Ohgr Oi Polloi Ok Go Ol' Dirty Bastard Old Man Gloom Oleander Olivia Newton-john Olympos Mons Omd On Thorns I Lay One Less Reason One Man Army One Voice Onyx Oomph! Open Skyz Opera Ix

Ophthalamia Opm Orange Goblin Ordalium Order Of The Ebon Hand Ordo Draconis Ordo Equilibrio Organized Konfusion Orphanage Orthodox Osi Otyg Our Last Night Outfield Outlandish Over It Overkill Oversoul Overthrow Oxymoron Ozma Ozzy Osbourne