The effect of gasoline sulfur content on urban ozone was estimated using the Urban Airshed Model (UAM) and exhaust emission measurements from the Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase II sulfur study. Ozone modeling was conducted for Los Angeles in year 2010 and Dallas-Fort Worth and New York in year 2005. Reducing fuel sulfur content reduced predicted ozone formation in all three cities. The light-duty vehicle contribution to predicted peak hourly ozone was reduced by 9, 16, and 8% in Los Angeles, Dallas-Fort Worth, and New York, respectively, when fuel sulfur content was reduced from 450 to 50 ppm. This corresponds to a reduction in total peak ozone from all sources of 0.8, 0.7, and 0.5% in Los Angeles, Dallas-Fort Worth, and New York, respectively, in year 2005/2010. There is uncertainty in these predicted effects; in particular, the effect of sulfur reduction expressed as a percentage of total peak ozone from all sources may be larger.