Petrol–electric transmission (UK English) or gasoline–electric transmission or gas–electric transmission (US English) is a transmission system for vehicles powered by petrol engines. Petrol-electric transmission was used for in , , and transport, in the early 20th century. After World War I, it was largely superseded by diesel-electric transmission, a similar transmission system used for diesel engines; but petrol-electric has become popular again in the 21st century in hybrid electric vehicles.