The CO2 tank is the most cost effecient way to opperate your paintball marker.Our CO2 tanks are DOT certified and stamped with a hydrostatic test date. Aluminum tanks are only good for 5 years after this date before they have to be retested. We gaurantee that our tanks are new and are currently in hydrostatic regulation. When buying from other dealers be aware that the tanks may be out of date. Tank manufacturer may vary depending on what we currently have in stock. This will not affect price, performance, or guartantee. We do this to ensure that you recieve you order as soon as possible.