http://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_.28petrol.29_Engines Modern gasoline engines have a maximum thermal efficiency of about 25% to 30% when used to power a car.
The most efficient type, direct injection Diesels, are able to reach an efficiency of about 40% in the engine speed range of idle to about 1,800 rpm.
上面講的是指最佳效率,當然車子引擎無法一直維持在最佳效率運轉,目前比較能接近這樣的運轉模式的就是油電車或是 Volt 那台靠汽油引擎發電、充電並純用馬達驅動的油電車。