Vertical Relations, Opportunism, and Welfare

This paper revisits the opportunism problem faced by an upstream monopolist contracting with several retailers over secret agreements, when contracts are linear. We characterize the equilibrium under secret contracts and compare it to that under public ones in a setting which allows for general forms of demand and retail competition. We find that market distortions are more severe under secret contracts than public ones if and only if retailers' actions are strategic complements. We also investigate the effect of opportunism on firms' profits. Our main results remain robust whether retailers hold passive or wary beliefs. Finally, we discuss the implications of our results for the antitrust analysis of information exchange between competing retailers, and for the empirical analysis of 'Nash-in-Nash' models.