Paintball guns run on pressurized gas. Early on in paintball, players only used CO2 because it was the only gas that was readily available. It worked, but not well in cold weather, and was not very consistent in pressure. Then someone came up with the idea to use nitrogen gas in mini scuba like tanks. They used nitrogen because it was another gas they could get from the local gas supply company at higher pressures. The nitrogen could be regulated in pressure and performed better in the guns for sure, but it was costly to transport and rent the nitrogen tanks from the gas supply company. The paintball industry looked for another gas alternative. Eventually scuba air compressors became affordable and now thats what all paintball fields use. Compressed air is easy on the guns internals and cost effective for the field owners. Some still call the tanks nitrogen tanks, but really they are now compressed air tanks, or high pressure air tanks. They are all the same, the only difference is the name. You want to use compressed air for sure. Its much better on the gun and performs better. Its works in colder weather and will make you gun more accurate.