Hold on to your wallet—the rental car company may charge you as much as $8 a gallon to refill the tank if you return the car with less than a full tank.

Allow enough time to fill up before returning the car. Count on paying a hefty surcharge—perhaps twice the cost at the pump, or more—if you forget or if you miss that last-chance gas station. And it doesn't matter whether the tank is half full—some companies will charge you an exorbitant rate for a full tank anyway.

Published September 15, 2008

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