Using a higher grade of gasoline than your car manufacturer recommends is like throwing money away. Premium gasoline costs 20 to 40 cents more per gallon than regular, and most experts agree that there is very little difference in quality between grades of gasoline. Another money-saving tip: When the gas tank is full and the pump handle shuts off automatically, do not add more gas. Gasoline needs room to expand, so if you top off your tank, the extra gasoline can evaporate into your car’s vapor collection system, causing your engine to run poorly. Sometimes, that extra gas is fed back into the gas station’s holding tank through its vapor recovery line. What’s more, overfilling your gas tank can cause harmful vapors to be released into the environment.