The Viking is like an Excalibur in that it will work on CO2 with some restrictions. To use CO2 you will need a reg on the CO2 tank. AKA suggests a Palmer Stabilizer with the female ASA on it. Out of the Palmer you will go into the Sidewinder. It's also recommended that you have an antisphon tube in your CO2 tank. You have to keep the CO2 liquid out of the gun.