It took around 3500 shots to empty my 20 oz co2 tank. For those wondering about how much gas it takes. I dont have any experience with hpa, but my understanding is that it isnt as super efficient as its hyped too be. These guns are a blast. The first time you wonder out to a game when you get one, and dont warn anyone, all your team mates turn around and look at you when you first start shooting it. The sound of it is amazing and sounds nothing like a sewing machine. And the blow back is amazing.