I used to buy the prepaid gas on my Kanas City/Des Moines runs, where I would land at MCI, and drive up to Des Moines. I could make it there and back and then coast that car back to the MCI rental returns on fumes.

When I did it with the Mercury Mystique, it was starting to knock as I pulled into the return line. I bet the staff couldn't even get to repark it without filling it up. That thing had a huge tank, the prepaid gas fee was about 37 dollars but I am sure it would have cost me 48-50 to fill it up locally, especially in Missouri.

It was always amusing to see the look on the attendants face.

I also managed a 5 hour run from Tulsa to Kanas City in a Honda Civic without filling up..

But when I don't drive much, such as on my Vegas and Orange County trips, I never prepay the gas.