Relative Responsibility for Cartel Damages

Cartel members are liable jointly and severally: any infringing firm may be litigated and forced to compensate victims on behalf of all members. EU law stipulates that co-infringers must pay internal redress in proportion to »relative responsibility for the harm caused.« We suggest to quantify this by invoking basic proportioning axioms and requiring that redress payments reflect causal links between actions and damages. This calls for application of the Shapley value. We prove that even symmetric firms may bear unequal responsibility for individual harm, characterize proportionings for linear market environments, and show that market shares typically fail to reflect relative responsibilities.