Skeleton production plans are developed for several scenarios. Weight estimates are made of each “base level.” Engines and transmissions are matched to the new weight, and a value of fuel economy, without other technological improvements, is determined. Fuel economy improvements due to other technological changes such as reduced aerodynamic drag, reduced tire rolling losses, the application of improved lubricants, etc., are added. Annual fuel economy estimates, by manufacturer, for each scenario, result. A brief review is included of the evolution of this methodology.