Researchers at the Swiss Federal Institute of Technology Zurich have developed a hybrid engine powered mostly by natural gas that could get the equivalent of 80 miles per gallon. The ultra-efficient engine, powered by a combination of natural gas and diesel, would achieve that lofty number when combined with a battery and electric motor, according to MIT Technology Review. The researchers said their hybrid engine would be more efficient and would have lower emissions than gasoline or diesel engines. The technology would add an estimated $8,000 to the cost of conventional gasoline vehicles, they said.