Collusion between two-sided platforms

We study the price and welfare effects of collusion between two-sided platforms and show that they depend on whether collusion occurs on both sides or a single side of the market, and whether users single-home or multi-home. Our most striking result is that one-sided collusion leads to lower (resp. higher) prices on the collusive (resp. competitive) side if the cross-group externalities exerted on the collusive side are positive and sufficiently strong. One-sided collusion may, therefore, benefit the users on the collusive side and harm the users on the competitive side. Our findings have implications regarding cartel detection and damages actions. (C) 2020 Elsevier B.V. All rights reserved.