OK I have an excellent question; How do you guys keep track of the Prius fuel mileage knowing the bladder in the tank changes size depending on the temperature?? Wouldn't that make it impossible to keep track of mileage? I live in Montreal Canada and the temperature varies from -35ÂºC(-31ÂºF) to +35ÂºC(95ÂºF) so the temperature is constantly changing throughout the year. Usually when you calculate your mileage, you take the distance traveled since your last fill up and the amount of fuel it takes to fill up the gas tank. But with the Prius gas tank, that accepts different amounts of fuel depending on the temperature, it throws that calculation all off. Since I see everyone on this site calculates their mileage and posts it up, how do you guys go about doing it. Is there a special technique? Thanks!