Federal clean air regulations have spawned a proliferation of motor fuel types that have created differentiated markets for motor fuels, increased the cost of supplying these fuels, and reduced the capacity of the supply infrastructure. In this paper we examine wholesale gasoline prices in 99 US cities over a time horizon of 204, weeks using a panel data regression model to explain fuel prices as a function of fuel attributes, the price of crude oil, and seasonal and city-market-specific effects. Our results show that fuel prices are related to the use of a special blend not widely available in the region and more costly to make, and the situation of the particular city market in relation to major refining centers or other sources of supply.