- O F F love
- O Yuki Conjugate
- O. Children
- O.L.D.
- Oathbreaker
- Obscenity Trial
- Obsidia
- Occul
- Octavia Sperati
- October Falls
- Odessa
- Odroerir
- Of a Mesh
- Officium Triste
- OffLimits
- OhGr
- Oil in the Eye
- Okk▼l† K▲††
- Ola Mesh
- Omdulö
- Omega Lithium
- Omnia
- On the Floor
- On Thorns I Lay
- One
- One Thousand Homo DJ'S
- One Way System
- One-Eyed Doll
- OneCyze Project
- Oneiroid Psychosis
- Oniric
- Onyria
- Oomph!
- oOoOO
- Open Ocean
- Opéra de Nuit
- Opera Diabolicus
- Opera IX
- Opera Multi Steel
- Opeth
- Ophelia’s Dream
- Opium Den
- Opium Jukebox
- Oracle
- Oracles
- Orange Juice
- Orange Sector
- Orchestral Manoeuvres in the Dark
- Ordo Equitum Solis
- Ordo Rosarius Equilibrio
- Orgy
- Origami Galaktika
- Orphanage
- Orphex
- Orplid
- Ost+Front
- Ostara
- Ostfront
- Ostia
- Otep
- Other Day
- Otras Voces
- Otto Dix
- Ötzi
- Ougenweide
- Our God Weeps
- Our Time Down Here
- Oval
- Overgament
- Ozric Tentacles
- Ozzy Osbourne