The aim of this paper is to investigate whether Islamic banks have greater market power than con-ventional banks. An Islamic bank, for example, might enjoy enhanced market power if a captive clientele adhering to religious principles permits it to charge higher prices. To measure market power, we compute Lerner indices for a sample of banks from 17 countries where Islamic and conventional banks coexist. Comparison of Lerner indices shows no significant difference between Islamic banks and conventional banks over the period 2000-2007. When including control variables, regression of Lerner indices even suggests that Islamic banks have less market power than conventional banks. A robustness check with the Rosse-Panzar model confirms that Islamic banks are no less competitive than conventional banks. Thus, any reduced market power of Islamic banks can be attributed to differences in norms and incentives.