Th is paper evaluates the performance on antitrust cases of the Chilean public enforcer (FNE by its acronym in Spanish). It presents an approach that frames its diff erences with private plaintiff s in terms of the eff ort that each of these mechanisms of enforcement should deliver during the trial. In a particular case, the presence of the FNE is used to draw the line between public and private enforcement, while the number of hearings is considered as a proxy of the joint eff ort delivered by the parties. Th e results show that the FNE outperforms private plaintiff s in a large number of cases where the eff ort of the parties is relatively low. However, within a small number of cases where the parties deliver a relatively high eff ort, the private plaintiff s are the ones who perform better. Th e paper argues that these trends are related with the structure of agency costs. Whereas private plaintiff s face a variable cost, depending on the number of victims whose coordination is required, the FNE works as a bureaucratic organization that has rather constant costs. Th e FNE has thus a comparative advantage in prosecuting off enses that involve a large number of victims, such as collusion. In contrast, private plaintiff s have the edge in cases involving a limited number of victims, such as dominance or predatory pricing. Diverging from recent studies, the paper concludes that the superiority of the FNE is only partial, and thus the policy should aim at bringing together both mechanisms of enforcement. Private and public enforcement does not behave as structural substitutes but as strategic complements. Hence, strengthening one at the expense of the other is plainly a bad idea.