Obtaining the maximum benefits from advanced fuel efficient engine oils will require that those oils not only provide fuel efficiency when new but also throughout the service interval for the oil. The effects of laboratory and engine aging on the ability of an oil containing a molybdenum dialkyldithiocarbamate (MoDTC) additive to provide reduced friction have been investigated. Results of these studies show that the friction reducing capability of this oil, as measured in a laboratory test, was lost prior to depletion of the MoDTC. Interactions between MoDTC and other additives were found to be important with regard to providing friction reduction. Implications for development of advanced oils that will provide lasting fuel efficiency benefits are discussed.