What is "tetraethyllead"

n. (context organic compound English) (alternative spelling of tetraethyl lead English)

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

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.

Innospec has claimed to be the last firm still making TEL, but TEL was apparently being produced illegally by several companies in China. As of June 2016 only Algeria, Yemen, and Iraq continue widespread use of leaded gasoline.