A survey by USA Today shows you could pay double market prices for gas if you don't refill the tank before returning the car. Rent-a-car companies charge from $5.79 per gallon up to $9.29 per gallon if the tank isn't full.
Rental agencies say avoid the high prices by pre-paying for a tank of gas when you rent the car or just fill it up yourself right before returning the car.
So where is the most expensive gas?
The LA Times found it in Hawaii -- $6.03 per gallon at a station on Maui
The cheapest was found in Casper, Wyoming -- $3.36 per gallon at a convenience store.