Tetraethyllead
Tetraethyllead (commonly styled tetraethyl lead), shortened to TEL, is a chemical compound with the formula (CH3CH2)4Pb. They add this into petro-fuel. It is first being mixed with gasoline beginning in the 1920s. This has caused increased vehicle performance and fuel economy. TEL had been identified chemically in the mid-19th century. In recent years, this chemical has been linked to climate change and is highly toxic.