It's 19.9 gal. Once the gauge shows true empty, you can still get about 50-70 miles out of it. I don't even go by the gauge any more. Just go by the Odometer and you'll be ok. I know that I get 300 -315 till empty, so I just refill at 285 and never have a problem. You might want to bring a gas can the first time you try this though.