Unleaded gasoline began in 1974. Lead began to be added to gasoline in the 1920s to reduce knocking or pinging within internal combustion engines. Due to the harmful effects of leaded gasoline on people's health as well as its negative environmental impact, leaded gasoline was phased out.
Lead was used as a gasoline additive as a lubricant for cylinder walls within the engine. As automobiles became more advanced, it was discovered that lead eroded catalytic converters. It was also determined that the fumes resulting from the burning lead in the gasoline accumulate on surrounding soil, and children can suffer damaging effects from exposure.