Avis/Budget have a gotcha fee called EZFuelTM that charges a flat $13.99 fee upon return for cars driven less than 75 miles, unless the renter proactively shows a refueling receipt. Yes, they trademarked a way to gouge customers. I have never heard this disclosed upon rental or return. This is US-specific and not all locations. The theory is to prevent people taking the car for a short drive and returning with the gas gauge showing full, though having consumed some fuel.
I received email notice that effective July 15, 2015, Hertz is implementing a matching Express Fuel $13.99 charge for rentals under 75 miles. Similarly, will not apply at all US locations, though no list is provided. A United-style meet the competition at the lowest common denominator move.
I have generally had fewer billing issues and phantom fees with Hertz than Avis. Here comes one to watch out. Always good practice to have a fuel receipt in hand upon any rental return.