Methane was a chemical compound. Kroll produced methane during its long periods of dormancy on Delta III. This was harvested by a refinery set up by humans. Such large quantities were gathered that the native Swampies' rights were ignored in order to gather it. (TV: The Power of Kroll)
The Vervoids could produce marsh gas, a methane derivative. (TV: Terror of the Vervoids)
The Eye of Gaar was made of ammonia and methane ice. (PROSE: Hot Ice)
The Thara relied on methane to survive. (PROSE: The Roots of Evil)