FOUNTAIN VALLEY, Calif., June 21, 2010 - After moving to the top of the U.S. Corporate Average Fuel Economy rankings in 2009, Hyundai remains firmly committed to leading the auto industry in fuel efficiency. With the introduction of a powertrain lineup exclusively consisting of four cylinder engines and six-speed transmissions, Hyundai's 2011 Sonata sedan became the most efficient vehicle in its class with an EPA rated highway mileage of 35 mpg.