A note on cost arrangement and market performance in a multi-product Cournot oligopoly

Model invariances have been used extensively to understand welfare and conduct consequences of firm heterogeneity in a one-product Cournot oligopoly. Nothing is known about the richer and more realistic context of firm heterogeneity in multi-product Cournot oligopoly. In this note, welfare in a two-product Cournot oligopoly is shown to increase (decrease) with an increase in correlation between unit costs when the outputs complement (substitute) in demand. A more qualified correlation structure is required for the result to apply in a three-product Cournot oligopoly when products complement in demand.