A standard paintball carbon dioxide tank is pressurized to 850 pounds per square inch. Paintball guns are commonly powered either by refillable carbon dioxide tanks, called bottles, or by disposable carbon dioxide cartridges. The carbon dioxide containers are filled with liquid carbon dioxide.
As the liquid carbon dioxide is released from the pressurized tank, it expands rapidly into a gas. This expansion propels the paint pellet out of the gun.
Paintball guns can also be powered by high-pressure air tanks. These contain air pressurized up to 3,000 to 4,500 pounds per square inch. An advantage of air over carbon dioxide is that air tanks do not get cold during heavy use.