Abstract:Analyses of the full social cost of motor vehicle use in the US often estimate an “oil import premium” that includes the military cost of defending oil supplies from the Persian Gulf. Estimates of this cost have ranged from essentially zero to upwards of a $1 per gallon (about $0.25 per liter). In this paper, we attempt to narrow this range, by carefully answering the question: “If the US highway transportation sector did not use oil, how much would the US federal government reduce its military commitment in the Persian Gulf?” We work towards our answer in five steps, accounting for interests not related to oil, the interests of other oil-consuming countries, the interests of producers apart from the interests of consumers, and the interests of non-highway users of oil. We estimate that were there no oil in the Persian Gulf, then US combined peacetime and wartime defense expenditures might be reduced in the long run by roughly $27–$73 billion per year (in 2004 dollars), of which roughly $6–$25 billion annually ($0.03–$0.15 per gallon or $0.01–$0.04 per liter) is attributable to motor-vehicle use.