Automotive manufacturers need information on refinery energy use and economics to identify the engine(s) that achieve maximum, vehicle miles from limited petroleum resources. To provide this information, we modeled a modern refinery producing varying amounts of automotive diesel fuel and producing gasolines covering a wide range in octane quality.Refinery energy consumption averages about 8% of the crude input. It declines slightly with increasing diesel fuel production and rises slightly with increasing gasoline octane number. However, differences in fuel energy utilization among engines are much larger than the variations in refinery energy use. When engine effects are considered, 7 to 8% more vehicle miles per barrel of crude could be achieved with gasoline having an Antiknock Index of 88–90 RM/2 and with maximum use of diesel vehicles.