Unleaded fuel was first introduced in 1972. By 1973, the Environmental Protection Agency demanded the phasing-out of the fuel additive tetraethyl lead. By the early 1980s, leaded fuel was completely phased out.
Unleaded gasoline was originally produced to protect the catalytic converters that first appeared in cars in 1975, and to squelch the EPA’s health concerns of the dangers associated with the THL additive. During experiments conducted at the General Motors laboratories, THL was first combined with gasoline in 1921 to solve engine knocking issues, increase octane levels and improve engine performance. By 1923, a leaded fuel was commercially available.