The majority of gas guns on the market take the propellant green gas. Green gas consists of propane and silicone oil. The added silicone allows the internal operating mechanisms to remain lubricated while being fired. Pure propane gas also works well as a propellant. Adapters for small disposable propane tanks allow you to fill your guns with off-the-shelf propane normally used for camp stoves. Other gas propellants include CO2 and red gas. Make sure you know what gas your gun requires before making a purchase.