Effects of Symmetry on Globalizing Separated Monopolies to a Nash-Cournot Oligopoly ∗

The effects of uniting separated markets, each monopolized by a producer, into a globalized oligopolistic market, which is regarded as a noncooperative game, or as a Cournot oligopoly game, are investigated. The cases where such globalization degrades the profits of all producers coincidently, are examined. Linear demand and production functions are considered. It is shown that in complete symmetry, the degree of such coincident profit degradation is strongest (the worst-case ratio), where the degree means the most modest ratio of the profit degradation among all producers. The system is in complete symmetry when the values of parameters describing all producers and markets are identical. On the other hand, in producer symmetry, the degree of coincident consumer surplus improvement is highest (the best-case ratio), where the degree means the lowest of the ratios of consumer surplus improvement among all (previously separated) markets. The system is in producer symmetry when the values of parameters describing all producers are identical.