From the Wired Auto Blog: The people’s car is taking the lead in high gas mileage vehicles. The “One-Liter” is a 660 lbs. 2 seater Volkswagen that gets 235 miles per gallon. It achieves this extremely low weight and high gas mileage with a carbon fiber body mated to a highly efficient one liter engine. VW had planned to hold off until 2012 to produce the vehicle citing the high cost of the carbon fiber. Since the carbon fiber technology has developed so quickly thanks to it’s use in many industries, including aerospace, the price of the material has come down to reasonable levels. Volkswagen only plans on producing small numbers of this niche vehicle, but it is a great study in what uber-high gas mileage requires.
http://blog.wired.com/cars/2008/07/laugh-at-high-g.html