The two mode hybrid system was developed by GM, Daimler-Chrysler, and Mercadez-Benz. Basically it has a pair of electric motors integrated with an automatic transmission. So they can drive the entire system by themselves if need be, or assist durring high torque applications. This coupled with variable valve timing, active fuel management makes for fuel economy typically seen in 4 cylinder camry.
http://www.chevrolet.com/hybrid/
Oh and the engine makes 367 horsepower @ 5500 rpm and 375 lb.-ft. of torque @ 4300 rpm