The determination of optimal fines to deter the formation or continuation of cartels is a major objective of competition policy. We provide an analysis of static and dynamic frameworks to characterize the restitution and deterrence properties of fines: cartel stability depends on their ability to prevent deviation by firms, while the benefit of a deviation depends on the fines to be imposed in case of detection by the antitrust authority. We show that the proper consideration of the dynamics of competition has a major impact on the determination of optimal dissuasive fines: our results suggest that a clear majority of fines imposed by the European Commission in recent years meet the deterrence objective.