"Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula (CH3CH2)4Pb.
TEL is a petro-fuel additive; first being mixed with gasoline (petrol) beginning in the 1920s as a patented octane rating booster that allowed engine compression to be raised substantially. This in turn caused increased vehicle performance (fuel economy).[3][4] TEL had been identified chemically in the mid-19th century, but its antiknock effectiveness was discovered in 1921 by the General Motors research laboratory, which had spent several years attempting to find an additive that was both highly effective and inexpensive. Among those GM also considered was ethanol, which was known to be widely available and inexpensive, but TEL was promoted because it was uniquely profitable to the patent holders and because the oil industry was generally hostile to ethanol.[5]"