The use of friction modifiers in fully formulated petroleum based motor oils for the purpose of increasing fuel efficiency in spark ignited engines has been investigated.Stationary engine test procedures were developed and used as a primary means for evaluating fuel economy potential of automotive oils. Fuel economy improvements with graphite-containing engine oils were greater in cyclic operation than in steady state operation. Vehicle dynamometer and controlled road tests with such engine oils also demonstrated improvements in fuel economy. Reduced viscosity was found to have a positive effect on fuel economy. Conventional oil components such as viscosity index improvers showed evidence for providing nominal differences in fuel economy. Substantial improvements in fuel economy were realized using dispersions of solid particles while retaining comparable viscosity characteristics for the oil.