Leaded gasoline is a type of fuel that contains tetraethyl lead, a compound added to improve engine performance and reduce knocking. It was widely used in vehicles from the 1920s until the late 20th century. However, lead is a toxic substance that can cause serious health problems, including neurological damage. Due to its harmful effects, the use of leaded gasoline has been phased out in many countries. The United States banned its use in 1996, and many other nations followed suit. Today, unleaded gasoline is the standard fuel for most vehicles, promoting better health and environmental safety.