Tractors generally use diesel engines rather than petrol engines because diesel engines are more reasonably priced and fuel-efficient than petrol engines. Tractor diesel engines generate higher torque and are useful for ploughing and transport. They also run longer than petrol engines and are more robust. Tractor diesel engines require less maintenance due to their simple design and lack of spark plugs. Still, another justification for running diesel engines in tractors is reduced pollution. For all these reasons, among tractors, diesel engines are quite favoured.