Do all paintball guns run on CO2?

Answer 1

All paintball guns require propellant, but some use HPA or high pressure air, instead. HPA tanks are more expensive and holds less shots, but are significantly more consistent (accurate) and easier and cheaper to refill. You can also tell how much you have left on a HPA tank.

Answer 2

All paintball parks allow co2, just based on the fact that its the most common type of air used for paintball.