When it is impossible to identify ex post the producer of a product causing harm, or the damage caused is indivisible although caused by multiple injurers, courts must apportion the total damage among tortfeasors. In this model we examine how such liability sharing rules affect the likelihood of tacit collusion. For this we use a standard Cournot oligopoly model where firms are collectively held liable for joint harm inflicted on third parties. With repeated market interaction and grim strategies, we investigate the sustainability of collusion to derive some policy implications.

This paper considers an oligopoly where …rms produce a joint and indivisible environmental harm as a by-product of their output. We …rst analyze the e¤ects on the equilibrium of alternative designs in environmental liability law, secondly, we discuss the rationale for "non-conventional" competition policies, i.e. more concerned with public interest such as the preservation of human health or environment. We study …rms decisions of care and output under various liability regimes (strict liability vs negligence) associated with alternative damages apportionment rules (per capita vs market share rule), and in some cases with damages multipliers. We …nd that basing an environmental liability law on the combination of strict liability, the per capita rule, and an "optimal" damages multiplier, is consistent with a conservative competition policy, focused on consumers surplus, since, weakening …rms' market power also increases aggregate expenditures in environment preservation and social welfare. In contrast, a shift to the market share rule, or to a negligence regime, may be consistent with a restriction of competition, since …rms'entry may instead lead to a decrease in aggregate environmental expenditures and losses of social welfare. Nevertheless the …ne tuning of the policy requires speci…c information from a Competition Authority, which we discuss as well.

Les clauses abusives sont interdites dans les contrats de consommation depuis 1978 et dans l’ensemble des contrats d’adhésion depuis 2016. Dans les deux cas, la sanction consiste à réputer la clause non écrite. Cette sanction ne permet pas de dissuader le rédacteur d’insérer des clauses abusives. Nous nous intéressons à une sanction alternative consistant à faire peser sur le rédacteur du contrat l’intégralité des frais de litige. Nous partons d’un modèle standard de concurrence à la Cournot, dans lequel nous intégrons des clauses abusives ainsi que les dépenses des parties en frais de litige. Nous montrons que la règle anglaise permet de dissuader le rédacteur du contrat d’insérer des clauses abusives. Classification JEL : K10, K12, K13, K41, D01.