Recent air quality regulations have mandated the use of reformulated gasoline and alternate fuels in motor vehicles. Reformulated fuels are intended to reduce both ozone-forming volatile organic compound (VOC) emissions and air toxic emissions from vehicles. A method that allows the determination of the individual contributions of a single VOC to the ozone formation in a complex VOC/NOx mixture is outlined and applied to eight potential reformulated fuel components. In calculations using a current comprehensive atmospheric chemical reaction mechanism a wide variety of organics are shown to be responsible for ozone production. The incremental reactivities of the fuel components, which are defined as the additional amount of ozone formed per amount of organic compound added to a base mixture, include both the direct production of ozone by the oxygenate itself and additional ozone produced by the VOC mixture when the oxygenate is added. The enhancement of ozone production attributable to the organic mixture upon adding the oxygenates is shown to be a result of changes to the organic free radical pool. Most of the fuel oxygenates have relatively low incremental reactivities due to their slow reaction rates and to the formation of relatively unreactive formate and acetate products. The more reactive fuel oxygenates are those containing ethyl groups, which react faster than their counterparts containing only methyl and tert-butyl groups.