My econ teacher told us that his father would always put in $10 of gas in his car no matter what the price of gas was. He showed that mathematically his father would come out on top. I know that there are a lot of ways people discuss about how much you should fill your tank (some say fill it up all the way you'll save, etc) but that has more to do with how the car works. The fixed rate of spending I believe was more tied into the fluctuation of gas prices. Does anyone know the formula/way to describe what my econ professor taught us? It's been too long and I forgot it.