The Prelude's tank is 15.9 gallons. The tank will never completely drain unless you really tried to drain it, so you'll have a couple gallons or so still in there before you fill it back up. The gauge doesn't necessarily show how much gas is left, it just shows how much gas is availible to the engine. If you're parked upwards on a hill and the gauge says E, you might not be able to start the car even though you still have gas in it.