Abstract:The introduction of unleaded gasoline and catalyst-equipped vehicles required numerous changes in U.S. transportation and energy systems. Simultaneous technological and operational changes in fuel production, distribution, and end-use systems had to be made, and the inherent resistance to change that characterizes complex sociotechnical systems had to be overcome. The transition to unleaded gasoline was unique in that it was instigated and orchestrated by federal rules and laws; market forces did not play a direct or major role. This government-orchestrated transition serves as a possible model for other countries that are contemplating the phasing out of lead in gasoline and, more generally, as a model for the United States and other countries for the introduction of non-petroleum fuels.