The adoption of significantly more stringent tailpipe emission standards is leading the domestic car manufacturers and oil companies to reexamine the composition of commercial gasolines. One offshoot of this examination is a cooperative inter-industry Auto/Oil Air Quality Improvement Research Program. This study will attempt to determine the potential reductions in total vehicle emissions and resultant improvements in air quality from the use of reformulated gasolines. One important aspect of the program is to determine the effect of variable aromatic and olefinic hydrocarbon content as well as variable levels of oxygenates on emission levels from a statistically-designed vehicle program.Much laboratory, engine and vehicle emission data has been generated over the past two decades that is potentially useful in interpreting the tailpipe emission patterns associated with proposed fuel composition changes. For sake of completeness, the role of fuel sulfur on tailpipe emissions will also be examined. This paper will examine these experimental data in order to provide guidelines for interpretation of fleet generated emission data and and to predict general directions of catalytic control strategy that should be considered when contemplating a change in gasoline composition. In addition, some new experimental data will be presented in this paper that relate to these general goals.