PHILADELPHIA (CBS) - If $4 a gallon gas prices aren’t enough to drive you crazy, wait until you see what happens if you don’t fill up your rental car tank.

A USA Today survey released this week found that, in some cases, rental car gas prices topped $9 a gallon for motorists who didn’t pre-pay and returned their cars without a full tank.

AAA Mid-Atlantic’s Jana Tidwell says if you play by the rental car companies’ rules, you’ll be fine, prices are otherwise in line with the going rate.

“It’s the folks who rent the car, drain the tank without pre-paying to refuel and don’t refill it before they return the vehicle. Those are the people that are incurring the high fuel prices, the $7, $8 , $9 a gallon fuel prices,” Tidwell said.

The rental companies say they’re not in the fuel business, though without fuel, they really can’t run their business. Still, it’s an inconvenience and an overhead for them to gas up the vehicles, so let the renter beware.

“I will fill it up myself,” one woman said. “I will bring it back full and pay the four dollars or whatever it is here.”

Reported by Paul Kurtz, KYW Newsradio