Bertrand competition under decreasing returns involves a wide interval of pure strategy Nash equilibrium prices. We first present results of experiments in which two, three and four identical firms repeatedly interact in this environment. More firms lead to lower average prices. However, prices remain substantially above the Walrasian level. With more than two firms the predominant market price is 24, a price not predicted by conventional equilibrium theories. This phenomenon can be captured by a simple imitation model and by a focal point explanation. For the long run, the model predicts that prices converge to the Walrasian outcome. We then use data from three new treatments to properly test the influence of imitation and focality. We find that both forces are present, but that imitation dominates in large markets with a long interaction.
Published as: 24. Pricing in Bertrand Competition with Increasing Marginal Costs in Games and Economic Behavior , Vol. 63, No. 1, 1--31, January, 2008