Deep Six is an underwater shooter, in which one or two players (alternating) control a diver hunting for treasure. The diver is equipped with a harpoon gun with unlimited ammunition, but there are air reserves that will get depleted over time. The game is segmented into three screens, the goal of the first two is to clear them of the small fish, respectively jellyfish that swim around. Larger enemies also appear which can be shot for bonus points. On the third screen lies the treasure, guarded by giant octopi. These cannot be killed, but they can be stunned. After gaining the treasure, bonus points are awarded and the game begins again.