An automobile that runs on both a conventional internal combustion engine, such as a gasoline engine, and an electric motor. The vehicle can operate at the optimum fuel efficiency by controlling each power source depending on driving conditions. Toyota Motor Corp. was the first to commercialize the technology with the Prius, released in December 1997. Because the technology can curb the use of the fuel-consuming engine, it can help reduce emissions of gases such as carbon dioxide, which is believed to cause global warming. Hybrid vehicles are cheaper to commercialize and produce than fuel cell vehicles that use hydrogen. Because of this, some in the auto industry project that the market for hybrid vehicles will grow to more than 3 million vehicles in 2010.