This article compares the level of fines actually imposed on cartel participants to the illicit gains captured by the firms and estimates a range of optimal restitution and dissuasive fines in each case. The results show that the fines imposed against cartels by the European Commission are, overall, moderate, regardless of the probability of detection. The article is based on a sample of sixty-four cartel decisions by the European Commission from 1975 to 2009 and a methodology that estimates optimal fines imposed on cartels on a case-by-case basis.