I know the website for fueleconomy.gov has been brought up before, but I just wanted to let people know it is useful for tracking your gas mileage. I use it all the time! I keep my receipts and write the trip odometer reading on it. Then, I log in to the website to record my fuel purchase. If you choose to share your fuel economy readings, it will be shown when you search for your particular car and see individual estimates. Doesn't show any personal info to the public though, which is good. Here is the link to the page which you can log on or register: https://www.fueleconomy.gov/mpg/MPG.do?action=garage

Hope y'all find this useful!