For a large class of demand and cost functions, we characterize the limit equilibrium set under Bertrand oligopoly when entry is exogenous. Unless average cost is constant, we find that the folk theorem of perfect competition necessarily fails. We also relate our results to those in Novshek and...

We examine if the folk theorem of perfect competition holds under Bertrand competition (when firms supply all demand), both when entry is exogenous, as well as when it is free. Inter alia, we also characterize the limit equilibrium sets.