In this paper, we report the results of an experiment aiming at comparing the American (Amnesty Plus) and the European leniency programs enforced by the competition authori- ties to fight multi-markets cartels. When a firm has been convicted due to the detection of a cartel, leniency means that the firm may obtain partial or full immunity if it cooperates and brings in evidence about this cartel. The US strengthened leniency programs for cartel in multimarket settings in order to incite the members of a first cartel previously detected and convicted to reveal their membership in cartels on other markets. With regard to the European program, Amnesty Plus may have a pro-collusive effect by encouraging the cartels' formation, as it reduces the expected cost from conviction. Our results do not confirm this procollusive effect. However, we show that the incentive to deviate is significantly higher under Amnesty Plus, both before and after a first cartel has been detected.