Like Stinger said, every car is different. You'll figure out pretty quick what kind of mileage you're getting. I think these gas tanks are pretty big, 15 gallons I believe. For whatever reason I get really good fuel economy, I get about 30mpg combined city and highway. And the reason why that is even more incredible is because my car is not really running right, it needs a tune-up pretty bad. Its bone stock, things like CAI will improve economy a little. But in general you will see around 25mpg combined, turbo's may be a little less. 23-24 perhaps.