What is the difference between returning a rental car without refueling so that the vendor does it and pre-paying to have the car refueled?

Seems sort of like two ways of looking at the same thing, doesn’t it? In fact, there are two different things and both come with hefty price tags for the convenience. If you return a car without filling it up first and you have not taken the pre-paid refueling option the vendor will charge you for the actual amount of gas used to fill up the tank – at a rate of $7-9 per gallon. If you select the pre-paid refueling option the vendor will charge you the local going rate for gas (or slightly less) – for an entire tank regardless of how much is actually used to fill the tank. As an example, let’s say you rented a vehicle with a 15 gallon tank and you used 5 gallons of gas. Without the pre-paid refueling option the average cost to you to have the vendor fill the tank will be $40 (5 x $8). With the pre-paid refueling option the average cost would be $54.75 (15 x $3.65 avg local cost per gallon). However, if you fill up the car yourself the average cost would be only $18.25 (5 x $3.65 local cost per gallon)!