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Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb(C2H5)4. It was widely used as a fuel additive for much of the 20th century, first being mixed with gasoline beginning in the 1920s. This "leaded gasoline" had an increased octane rating that allowed engine compression to be raised substantially and in turn increased vehicle performance and fuel economy. TEL was first synthesised by German chemist Carl Jacob Löwig in 1853. American chemical engineer Thomas Midgley Jr., who was working for the U.S. corporation General Motors, was the first to discover its effectiveness as an antiknock agent in 1921, after spending several years attempting to find an additive that was both highly effective and inexpensive. In the mid-20th century, scientists discovered TEL caused lead poisoning and was toxic to the human brain, especially in children. The United States and many other countries began phasing out the use of TEL in automotive fuel in the 1970s. By the early 2000s, most countries had completely banned the use of TEL in gasoline. Since 2011, leaded gasoline has been banned in every country. A 2011 study backed by the United Nations estimated that the removal of TEL had resulted in $2.4 trillion in annual benefits, and 1.2 million fewer premature deaths. Despite being banned from use in automotive fuel, TEL is sometimes still used in certain grades of aviation fuel. Innospec has claimed to be the last firm legally making TEL but, as of 2013, TEL was being produced illegally by several companies in China. In July 2021, the sale of leaded gasoline for cars was completely phased out worldwide, prompting the United Nations Environment Programme (UNEP) to declare an "official end" of its use in cars on August 30, 2021.