Avgas (aviation gasoline) is an aviation fuel with spark-ignited internal combustion engines. In aviation, Avgas is distinguished from conventional gasoline (petrol) used in motor vehicles, termed mogas (motor gasoline). Unlike motor gasoline, formulated since the 1970s to allow platinum-content catalytic converters for pollution reduction, the most commonly used grades of avgas still contain tetraethyllead (TEL), a toxic substance used to prevent engine knocking (premature detonation). Ongoing experiments aim to reduce or eliminate the use of TEL in aviation gasoline.