Oak Roots	http://www.metal-archives.com/bands/Oak_Roots/3540312275	Folk Metal	Italy
Obituary	http://www.metal-archives.com/bands/Obituary/165	Death Metal	United States
Obsequy	http://www.metal-archives.com/bands/Obsequy/3540296589	Progressive/Death Metal	United States
Obsidian Sea	http://www.metal-archives.com/bands/Obsidian_Sea/3540302433	Doom Metal	Bulgaria
October Tide	http://www.metal-archives.com/bands/October_Tide/2337	Melodic Doom/Death Metal	Sweden
Odem Arcarum	http://www.metal-archives.com/bands/Odem_Arcarum/19432	Black Metal	Germany
Odroerir	http://www.metal-archives.com/bands/Odroerir/6932	Folk Metal	Germany
Offending	http://www.metal-archives.com/bands/Offending/64160	Brutal Death Metal	France
Offertorium	http://www.metal-archives.com/bands/Offertorium/3540269025	Black Metal	Brazil
Officium Triste	http://www.metal-archives.com/bands/Officium_Triste/2517	Death/Doom Metal	Netherlands
Okera	http://www.metal-archives.com/bands/Okera/3540331033	Melodic Death/Doom Metal	Australia
Oktober	http://www.metal-archives.com/bands/Oktober/39839	Black Metal	United States
Old Corpse Road	http://www.metal-archives.com/bands/Old_Corpse_Road/3540276630	Black/Folk Metal	United Kingdom
Omega Massif	http://www.metal-archives.com/bands/Omega_Massif/56578	Sludge Metal	Germany
Omit	http://www.metal-archives.com/bands/Omit/3540329804	Doom Metal	Norway
Ondskapt	http://www.metal-archives.com/bands/Ondskapt/10188	Black Metal	Sweden
Ophidian I	http://www.metal-archives.com/bands/Ophidian_I/3540347460	Technical Death Metal	Iceland
Ophis	http://www.metal-archives.com/bands/Ophis/13185	Death/Doom Metal	Germany
Ophthalamia	http://www.metal-archives.com/bands/Ophthalamia/4874	Black Metal	Sweden
Oranssi Pazuzu	http://www.metal-archives.com/bands/Oranssi_Pazuzu/3540279710	Psychedelic Black Metal	Finland
Orchidectomy	http://www.metal-archives.com/bands/Orchidectomy/36306	Brutal Death Metal	Canada
Ordo Draconis	http://www.metal-archives.com/bands/Ordo_Draconis/4604	Black Metal/Post-Black Metal	Netherlands
Ordo Templi Orientis	http://www.metal-archives.com/bands/Ordo_Templi_Orientis/3540272740	Atmospheric/Depressive Black Metal	Belarus
Origin	http://www.metal-archives.com/bands/Origin/79	Technical Brutal Death Metal	United States
Orphaned Land	http://www.metal-archives.com/bands/Orphaned_Land/2309	Doom/Death/Middle Eastern Folk Metal (early), Middle Eastern Folk Metal (later)	Israel
Orrery	http://www.metal-archives.com/bands/Orrery/122828	Black Metal	Australia
Osamenta	http://www.metal-archives.com/bands/Osamenta/82552	Death Metal	Puerto Rico
Oskord	http://www.metal-archives.com/bands/Oskord/3540336145	Folk Metal	Ukraine
Ossian	http://www.metal-archives.com/bands/Ossian/66685	Black/Death Metal	Turkey
Otyg	http://www.metal-archives.com/bands/Otyg/80	Folk Metal	Sweden
Ov Hollowness	http://www.metal-archives.com/bands/Ov_Hollowness/3540312456	Atmospheric/Ambient Black Metal	Canada