The CO2 tank comes empty and must be filled before first use. Most cities have places that will either fill or swap tanks. Medical supply companies like Norco offer this service. Also, you can ask your local beer distributor where they recommend, or ask your favorite bar who provides their CO2. As far as how long they last, that's determined by how frequently you use it and whether or not you remember to close the tank when the beer runs dry, between kegs. I am currently on my 1st tank and 3rd keg. It cost me $30 for the gas.