Tetraethyllead

Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula (CH₃CH₂)₄Pb.

TEL was mixed with gasoline (petrol) beginning in the 1920s as a patented octane rating booster that allowed engine compression to be raised substantially, which in turn increased vehicle performance or fuel economy. TEL in automotive fuel was phased out starting in the U.S. in the mid-1970s because of its cumulative neurotoxicity and its damaging effect on catalytic converters. When present in fuel, TEL is also the main cause of spark plug fouling. TEL is still used as an additive in some grades of aviation gasoline, and in some developing countries.