- Over Serenity (Alternative Metal-France) - Other name : OS
- Ocean Sleeper (Metalcore-Australia) - Other name : OS
- Outspoken Silence (Post Hardcore-United-Kingdom) - Other name : OS
- Oh, Sleeper (Metalcore-USA) - Other name : OS
- Orange Sky (Metal-Trinidad-and-Tobago) - Other name : OS
- Os Capial (Grindcore-Brazil)
- Dias De Raiva (Hardcore-Portugal) - Other name : ODDR, Os Dias De Raiva
- Os-Croix (Black Metal-France)
- Os'Satur (Metalcore-France)
- Osada Vida (Heavy Rock-Poland)
- Osairis (Heavy Metal-Singapore)
- Osaja Tir (Death Metal-Afghanistan)
- Osamenta (PR) (Death Metal-Puerto-Rico)
- Osamenta (ECU) (Thrash Black-Ecuador)
- Osamenta (ARG) (Thrash Metal-Argentina)
- Of Saints And Sinners (Hardcore-Germany) - Other name : OSAS
- Of Silence And Salvation (Metalcore-USA) - Other name : OSAS
- Osatia (Post Hardcore-USA)
- One Step Beyond (AUS) (Alternativ Death-Australia) - Other name : OSB
- Oscillator (Deathcore-USA) - Other name : Øscillatör
- Oscult (Black Metal-Germany)
- Osculum (Black Metal-Mexico)
- Osculum Infame (FRA) (Black Metal-France)
- Osculum Infame (BRA) (Black Death-Brazil)
- Osculum Infame (GRC) (Black Metal-Greece)
- Osculum Obscenum (CHL) (Death Metal-Chile)
- Osculum Obscenum (BRA) (Brutal Black-Brazil)
- Osculum Serpentis (Black Metal-France)
- Oscura Cepa (Heavy Metal-Argentina)
- Oscura Nocturna (Atmospheric Gothic-Guatemala)
- Human Dirge (Progressive Death-Italy) - Other name : ex-Oscura Poetry
- Oscura Tentación (Heavy Metal-Spain)
- Oscuriam (Symphonic Metal-Mexico) - Other name : Dark Matter, ex-Ecliptika
- Oscuridad (COL) (Black Metal-Colombia)
- Oscuro Diciembre (Metalcore-Mexico)
- Oscuro Mito (Folk black-Bolivia)
- Oscuro Profano (Atmospheric Black-Chile)
- Oscuros (Black Metal-USA)
- Oscurus Infernal (Black Metal-Ecuador)
- One Starving Day (Hardcore-Italy) - Other name : OSD
- Osdizx (Black Death-Germany)
- Our Survival Depends On Us (Sludge Doom-Austria) - Other name : OSDOU
- Ose (Black Metal-USA)
- Our Souls Evolve (Metalcore-Canada) - Other name : OSE
- One Size Fits All (Metalcore-France) - Other name : OSFA
- One Shot For All (Deathcore-Russia) - Other name : OSFA
- On Solid Ground (Deathcore-USA) - Other name : OSG
- Osgiliath (MEX) (Atmospheric Black-Mexico)
- Osgiliath (FRA) (Epic Black-France)
- Osh (Death Thrash-Germany)
- Oshiego (Thrash Death-Singapore)
- Office Of Strategic Influence (Progressive Metal-USA) - Other name : OSI
- Ordo Spiritum Invictis (Black Metal-France) - Other name : OSI
- Osi And The Jupiter (Pagan Folk-USA)
- Osiah (Deathcore-United-Kingdom)
- Osian (Gothic Dark-Italy)
- Osirex (Ambiant Black-USA)
- Osirion (Thrash Black-France)
- Osiris (ARG) (Symphonic power-Argentina)
- Osiris (CAN) (Heavy Metal-Canada)
- Osiris (NL) (Technical Thrash-Netherlands)
- C Of E (Progressive Metal-Netherlands) - Other name : ex-Osiris, ex-Circle Of Emotion
- Osiris (UK) (Power Metal-United-Kingdom)
- Osiris (EGY) (Black Metal-Egypt)
- Osiris (ITA) (Folk black-Italy)
- Osiris Rising (Symphonic Heavy-USA)
- Osiris Troopz (Death Metal-Indonesia)
- Oskal (Black Metal-Russia)
- Oskord (Folk Metal-Ukraine)
- Oskorei (BEL) (Brutal Black-Belgium)
- Oskorei (USA) (Death Thrash-USA)
- Oskorei (GER) (Black Metal-Germany)
- Oskoreien (Black Metal-USA)
- Oskrnavitelj (Black Metal-Serbia)
- Oskryf (Drone-Finland)
- Overstrange Mood (Progressive Metal-France) - Other name : OSM
- Oklahoma Swamp Monster (Stoner-France) - Other name : OSM
- Osmed (Brutal Death-Indonesia)
- Osmi Putnik (Heavy Metal-Croatia)
- Osmium (NZ) (Alternative Metal-New-Zealand)
- Osmium (USA) (Thrash Metal-USA)
- Osmium Grid (Death'n'Roll-Australia)
- Osmium Guillotine (Heavy Metal-United-Kingdom) - Other name : OG
- Osmose (Black Metal-Belgium)
- Hydra (USA-1) (Southern Rock-USA) - Other name : ex-Noah Mayflower, ex-Osmosis
- Osmosis (Death Black-Spain)
- Osning (Atmospheric Black-Germany)
- Osobrom (Black Death-Chile)
- Osoka (Atmospheric Sludge-Russia)
- Osraige (Black Metal-United-Kingdom)
- Oss Nebes (Black Metal-Russia)
- Ossadogva (Black Metal-Ukraine)
- Ossaert (Black Metal-Netherlands)
- Ossario (Thrash Black-Italy)
- Ossarios (Thrash Death-Brazil)
- Ossarivm (Death Metal-Portugal) - Other name : Ossarium
- Ossarium (Death Doom-Germany)
- Ossastorium (Melodic Death-Lithuania)
- Osschaert (Black Metal-Netherlands)
- Ossea Cyphus (Black Metal-USA)
- Ossein (Atmospheric Black-USA)
- Osseltion (Technical Death-Italy)
- Ossements (Ambiant Black-Canada)
- Osserp (Death Grind-Spain)
- Ossian (Heavy Metal-Hungary)
- Ossidiana (Symphonic Metal-Italy)
- Ossification (Death Metal-USA)
- Ossilegium (Black Metal-USA)
- Ossimoro (Stoner-Italy)
- Ossonor (Symphonic Metal-France)
- Ossuaire (CAN) (Black Metal-Canada)
- Ossuaire (FRA) (Death Metal-France)
- Ossuarist (Death Grind-USA)
- Ossuarium (Death Metal-USA)
- Ossuary (USA) (Black Death-USA)
- Ossuary (SGP) (Thrash Metal-Singapore)
- Ossuary (COL) (Death Metal-Colombia)
- Ossuary (BLR) (Death Metal-Belarus)
- Ossuary (URU) (Death Metal-Uruguay)
- Ossuary Anex (Brutal Death-Russia)
- Ossuary Insane (Death Metal-USA)
- Ossuary (USA-2) (Death Metal-USA)
- Ossuary (USA-3) (Death Metal-USA)
- Ossuary Vault (Doom Black-Canada)
- OSSY (Heavy Metal-Finland)
- Ossyris (Heavy Metal-Spain)
- One Shot Thrill (Electro Metal-USA) - Other name : OST
- Ost Est Ima (Death Metal-Canada)
- Ostfront (GER) (Industrial Metal-Germany) - Other name : Ost+Front
- Ostanes (Experimental Metal-Iran)
- Ostend Powers (Nu Metal-Belgium)
- Osteocondrodisplasia (Grindcore-Argentina)
- Ostfront (UKR) (Ambiant Black-Ukraine)
- Ostinato (Experimental Metal-USA)
- Ostitto (Deathcore-Bangladesh)
- Ostium (Black Metal-France)
- One Step To Kill (Deathcore-Ukraine) - Other name : OSTK
- Ostots (Black Metal-Spain)
- Ostracism (Black Metal-USA)
- Ostracist (Gothic Metal-Greece)
- Ostracized (Thrash Death-France)
- Ostrogoth (Heavy Metal-Belgium)
- Ostrova (Alternative Metal-Spain)
- Ostura (Symphonic power-Lebanon)
- Unkreuz (Black Metal-Germany) - Other name : ex-Ostwind
- Osukaru (Hard Rock-Sweden)
- Osvajaci (Heavy Metal-Serbia)
- Osyris (Power Metal-Germany)
- Osyron (Progressive Metal-Canada)
- Osyth (Black Metal-Mexico)
