With weak law‐enforcement institutions, a positive shock to the value of natural resources may increase demand for private protection and opportunities for rent appropriation through extortion, favouring the emergence of mafia‐type organisations. We test this hypothesis by investigating the emergence of the mafia in twentieth century Sicily, where a severe lack of state property‐rights enforcement coincided with a steep rise in international demand for sulphur, Sicily's most valuable export commodity. Using historical data on the early incidence of mafia activity and on the distribution of sulphur reserves, we document that the mafia was more present in municipalities with greater sulphur availability.