antitrust authorities in each market. We are concerned with how the sustainability of collusion in one local market is affected … by the existence of collusion in other markets when they are linked by demand relationships. The interdependence of … collusion sustainability across markets leads to potential externalities in antitrust enforcement across jurisdictions. As a …

, collusion …

stakes of collusion. On the other hand, it creates an asymmetry between the integrated firm and the unintegrated competitors … cooperative equilibrium, which potentially harms collusion. As we show, the optimal collusive profit-sharing agreement takes care … the asymmetries in the non cooperative state. As a result, vertical integration generally favors collusion …