Methane

Methane is a liquid often found underground and sometimes in the surface. In Titan, a moon of Saturn which is enterable, all lakes are Methane. See Rocket for more information.

Methane, if found on any world with sufficient oxygen (meaning purple-blue skies) can explode for up to 5x5 tiles if a fire source is dropped on it (explosions, flamethrower, fire blocks, etc.)