High Quality Content by WIKIPEDIA articles! Tetraethyllead (common name tetraethyl lead), abbreviated TEL, is an organolead compound with the formula (CH3CH2)4Pb. It was admixed with gasoline (petrol) beginning in the 1920s as an inexpensive octane booster which allowed engine compression to be raised substantially, which in turn increased vehicle performance and fuel economy. TEL was phased out starting in the US in the mid-1970s because of its neurotoxicity and its deleterious effect on catalytic converters. It is still used as an additive in aviation fuel for piston engine-powered aircraft.