The optimal product mix for a monopolist in the presence of congestion effects: A model and some results

The paper develops a model of product differentiation in which the quality of a product may be negatively affected by the number of consumers buying it, as it is the case for any good affected by congestion. It is shown that for any positive degree of heterogeneity among the consumers, a monopolist will always find it more profitable to differentiate, i.e., to sell more than one quality of the product at different prices.