• Oak, Ash & Thorn (Pagan/Folk-metal)
• Oakenshield (Viking/Folk-metal)
• ‡ Oakhelm (Pagan Folk Black Metal)
• Oak Pantheon (Folk/Pagan/Black Metal)
• ‡ Oak Roots (Folk-metal)
• Obereg (Folk/Pagan Metal)
• Obscurity (Pagan/Viking Metal)
• Ocelon (Celtic Folk-metal)
• ‡ ODR (Folk-metal)
• Odraedir (Pagan/Folk-metal)
• Odroerir (Folk-metal)
• Ofärd (Folk-metal)
• ‡ Ogmiös (Folk-metal)
• O’Hamsters (Celtic Punk)
• ‡ Ol’ Jolly Roger (Pirate Metal)
• Omiors (Occitan metal)
• Omut (Folk-metal)
• Onkel Hryum (Trash/Death/Folk-metal)
• Open Access (Folk-metal)
• OracleVuh (Folk-metal)
• Oprich (Folk-metal)
• Orphaned Land (Folk-metal)
• Oscenrad (Anglo-Saxon Heathen Metal)
• ‡ Oskord (Folk-metal)
• ‡ Othalan (Folk-metal)
• ‡ Otyg (Folk-metal)