Methane is an odorless, simple hydrocarbon. The chemical formula is CH4.
At normal temperature it is less dense than air. It melts at –183°C and boils at –164°C.
It exists on many planets, such as Earth, Titan, and many others. The atmosphere of a Class K planet (such as Theta 116 VIII) consists of methane, nitrogen and liquid neon (TNG: "The Royale").
In 2364, an accidental explosion from a methane-like gas occured on the Sigma III colony Quadra Sigma III. (TNG: "Hide and Q")
In 2151, Klaang, a Klingon courier, was responsible for the destruction of a grain silo on Earth which belonged to a human farmer named Moore. The silo contained methane, which was released when the building exploded. (ENT: "Broken Bow")
The Axanar breathe a nitrogen-methane atmosphere. (ENT: "Fight or Flight")
An Oort cloud is composed of methane.