During World War II the Allies controlled Spain's oil supply in order to limit Spain's support for the Axis. This experiment with sanctions is unusually informative because a wide range of policies was tried over a long period. Three episodes are of special interest: (1) a total embargo on oil for Spain in August 1940 that was surprisingly successful in dissuading Spain from joining the Axis; (2) a period of reduced supplies in 1941–42, which we call ‘the Squeeze’, that was only partially successful in reversing Spanish policies favouring the Axis; and (3) a second total embargo early in 1944, which proved a disappointment for the Allies, and that produced a rift between Churchill and Roosevelt. Our analysis is based on new monthly estimates of Spain's imports of gasoline and other petroleum products that we describe in the text and report in the Appendix. These estimates allow us to draw a clearer picture of the oil sanctions than has been possible in the past.