This paper argues that since the supply of oil in the ground is inelastic, the incidence of a sales tax on oil, maintained forever at a fixed rate, would fall entirely on the oil-suppliers. In the world economy, however, the elasticity of supply of oil to a single country depends on that country’s imports as a share of world output and on the elasticity of demand for that country. The paper calculates optimal tax rates for a country as a function of these variables and estimates optimal oil tax rates for the U.S., for some OECD countries separately, and for the U.S. plus the OECD collectively. Current U.S. tax rates are shown to be far below optimal values.