The appeals process is an important mechanism to correct legal errors and to improve existing laws and regulations. We use the data of 467 firm groups that participated in 88 cartels convicted by the European Commission between 2000 and 2012 to study both the characteristics of firm groups filing an appeal and the factors that determine their successfulness in terms of fine reduction. Applying a discrete choice and a two‐stage hurdle model, we find that while some characteristics—particularly the reform of the fine guidelines—only affect the probability of filing an appeal, other factors, such as the size of the fine imposed, in connection with characteristics such as ringleader, repeat offender, or leniency applicant, influence both the probability and the success of an appeal. We build on these results to derive conclusions for both firms and public policymakers.