I know what you're thinking, how hard can it be to determine gas mileage, right?  Well, some people just are not familiar with the calculation used to determine gas mileage.

Here is a simple way to figure it out:

Total miles driven per tank of gas divided by total number of gallons to fill the gas tank.  i.e. 300 miles ÷ 12.6 gallons = 23.81 miles/gallon.

Remember, the way you drive effects your gas mileage.  If you accelerate hard, brake late, and drive above the speed limit your gas mileage will most likely decrease.  However, if you accelerate steadily and brake in a reasonable amount of time, plus maintain consistent speeds, your gas mileage will increase.  It is also important that you use the correct octane in your gas.

Now, if you are a 16 year old boy, or girl, and you feel the need for speed or to beat your buddy's ass off the line, than you can count on spending more at the pump, more often.  For those who find it necessary to brake at the very last second, not only will you be replacing brake pads frequently, but you will also hinder optimal fuel economy.  But then again, you're only 16 once!