A paintball marker, also known as a paintball gun, is the main piece of equipment in the sport of paintball. Markers use an expanding gas, such as carbon dioxide (CO2) or compressed air, to propel paintballs through the barrel. The term "marker" is derived from its original use as a means for forestry personnel to mark trees and ranchers to mark wandering cattle.The muzzle velocity of paintball markers is approximately 90 m/s (300 ft/s).