We augment the multi-market collusion model of Bernheim and Whinston (1990) by allowing for firm entry into, and exit from, individual markets. We show that this gives rise to a new mechanism by which a cartel can sustain a collusive agreement: Collusion at the extensive margin whereby firms...

We provide a new model that generates persistent performance differences amongst seemingly similar enterprises. Our model provides a mechanism whereby efficient incumbent rivals can give permission for an inefficient firm to exist in the presence of efficient entrants. We demonstrate that, in a...