ou've heard of hybrids, electric cars and vehicles that can run on vegetable oil. But of all the contenders in the quest to produce the ultimate fuel-efficient car, this could be the first one to let you say, fill it up with air. That's the idea behind the compressed air car, which backers say could achieve a fuel economy of 106 miles per gallon. Plenty of skepticism exists, but with many Americans trying to escape sticker shock at the gas pump, the concept is generating buzz. More →