- 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)
- Oskord (Folk-metal) ‡
- Othalan (Folk-metal) ‡
- Otyg (Folk-metal) ‡