HFC Darkhawk Heavyweight Gas Blowback Airsoft Pistol

"what type of gas does it take? CO2 or green gas? This might be my first gas pistol. I've always thought it would be obnoxious to have to keep buying gas but my friends have showed me otherwise and This seems good enough to deal with the range that i would be shooting from. Most spring pistols just curve up and aren't as durable as guns like this one.