- October Grey (Progressive Metal-United-Kingdom)
- Octobre (Black Metal-Canada)
- October (Black Metal-Spain)
- Odd Project (Metalcore-USA)
- Orphan Project (Progressive Metal-USA)
- Octomber (Doom Black-Russia)
- October Tide (Death Doom-Sweden)
- October File (Post Hardcore-United-Kingdom)
- October Noir (Gothic Doom-USA)
- Overreact (Crossover-France)