Published: May 10, 2011 9:08 PM EDT
Updated: May 10, 2011 6:03 PM EDT

FORT MYERS, Fla.- Thanks to high gas prices, used car dealerships are having a hard time keeping fuel efficient cars stocked on their lots. The spike in demand is costing dealerships-- and consumers-- more money.

Compact cars are flying off the lots, causing their price tags to no longer match their size. Germain Auto Advantage says the cost of small used cars is up 13% from last year.

"It's much more expensive. Their values are going up every week instead of dropping," Auto Advantage store manager Rick Gatliff said Tuesday.

Fuel efficient cars are the hardest to keep in stock right now. Dealers say getting your hands on something like a used Toyota Prius is going to cost on average about $1,500 more than a month ago.

Despite the price hike, many used car dealerships are struggling to meet drivers demand for more fuel efficient models.

"I usually keep about 20% of my inventory of small, entry level cars. Right now, we're calling out to our buyers, and we can't hardly find them," Gatliff said.

As for those gas guzzlers, Victory Layne Chevrolet says they're now harder to move.

"Trucks have gotten a little soft. You still have you have your truck buyers who are going to have their Tahoe's, Surburban's, their family vehicles. It has slowed a little," Mark Baldassarre of Victory Layne Chevrolet said.

If you're looking to trade in your car for a new one, dealerships say it's a seller's market... especially if your ride gets good gas mileage.

"If you have the right car, it is worth more money than it was 6 months ago. More people are coming in and selling their cars for that very reason," Baldassarre said Tuesday.

Experts say the devastating earthquake in Japan is part to blame for the higher cost of used cars. As dealerships experience shortages of new models due to Japan's production slowdown, more consumers are looking to their used counterparts.