I know there is a mileage log but I thought at first anyway it might help to put some numbers here. I just put in my second tank. I had an indicated 43.9 mpg with 11.29 gallons used for 496.3 miles. That was indicated however it took 12.254 gallons to fill it up for an actual 40.5 mpg. The first tank seemed pretty close to indicated but this is the first one that I filled it up both times. I know there can be some variance on the pump shutoff but you wouldn't think the indicated vs actual fuel usage would be off by almost a gallon.