An essential part of your paintball gear is your air tank.  Paintball guns are powered by portable tanks filled with either CO2 or high pressured air.  The tanks come in various sizes with the larger carrying more air and therefore offering more shots.  CO2 tanks are cheaper and more commonly used; many starter paintball packages come with a CO2 tank as they are generally what most beginners start with.  High pressure air tanks cost a bit more, however they are lighter, easier to refill and improve your marker’s efficiency and reliability.  Most paintball guns can use either CO2 or high pressure air without any modification.