Pretty much every gas used apart from duster gas as a propelent for airsoft is propane/Butaine based
I normally use garder power up, that's 100%propane without the Smell and silicone oil added
C and p
From wiki
Green Gas is used as a propellant for airsoft guns. It is an alternative source of power as opposed to spring- or motor-driven airsoft weapons.
In 2004, it was determined by Carlton Chong (of Airsoft Innovations) through gas chromatograph analysis that green gas is in fact a mixture of propane, silicon oil, and odour modificants.[1] This discovery prompted his development of a propane adaptor, allowing users to administer their own green gas derivatives using retail propane and silicone oil.