Empirical research shows that natural resources have a detrimental effect on economic growth, a phenomenon known as the “resource curse”. Competition between influence groups for access to the resource rents, that is, rent-seeking, is often blamed for this curse. In this paper we dig deeper into the link between political competition and the resource curse by studying the case of Iran from 1960-2007. We present a theoretical model demonstrating how the effect of rents on the economy depends on the balance of political power. The model shows that an increase in rents may lead to a sharp reduction in income when the distribution of power between influence groups is relatively balanced. The empirical evidence confirms the predictions of the model.