Most modern microlights use purpose built engines designed and built in Austria by Rotax. Most of these engines are two strokes and use ordinary 4 star petrol. The power output from a modern microlight engine can be as much as that from a small car. The drive to the propeller is via a gearbox. This is to reduce the RPM to allow the propeller to run at a lower speed than the engine. This makes the aircraft much quieter as most of the noise is generated by the propeller. There are other types of engines in use, but the Rotax units are by far the most popular at the moment.