Gas-powered guns use pressurized gases like propane and HFC134a refrigerant to propel BBs, or little round metal pellets. These guns are commonly known as BB guns. Carbon dioxide and nitrogen may also be used and are more common. Environment friendly Freon (a variety of nonflammable gaseous or liquid fluorinated hydrocarbons) may also be used, but the type of gas used for operating these guns may also depend on the type of gun. Gas power is more commonly used in smaller handguns like pistols. Gas is either injected into a reservoir within the gun or attached to an exterior tank.

Gas-powered guns have a few advantages, which include adjustable velocities and blowback features. In the blowback mechanism, onboard or magazine-stored gas storage system is used to propel the pellets. The same compressed air that propels the pellet is used to pull back the slide. These airsoft guns are known as gas blowback guns or GBBs. Because of this blowback feature, BBGs are capable of automatic or semi-automatic fire. This means that the magazine can be emptied as fast as the trigger is squeezed, and be easily reloaded by inserting a new magazine.

Green gas, normally a mixture of propane and silicone oil, is the recommended and most commonly used propellant in gas-powered Airsoft guns. HFC134a refrigerant is also widely used but is less powerful and not suitable for colder climates, where the gas may become insufficient to operate the guns. However, excessive use of Green gas may be harmful to guns that cannot handle the exceptional power.