Private firms and a public firm sometimes form an oligopoly market, and compete one another. Especially on the European Continent, we can find many cases even now after the trend of the privatization, and we Japanese also have private banks and public post office in financial market. The so-called “mixed oligopoly (MO) ” have aimed at the revivals and progresses of some industries (firms) or the securance of employments depending on ample funds of the state, but after Merrill and Schneider (1966), some examine its validity as means of market intervention instead of the regulation on private firms or the public monopoly; and there the difference of their action principles, not the funds of the public firm, became an important matter.
In this paper, after pointing out the validity of MO in use of the simple Cournot model, we examine whether the validity is preserved when production efficiencies are different between the two types of firms, and when the number of the private firm increases form 1 to
n-1. Also, we focus on the profit (constraint), which is often neglected in such studies, and extend to examine whether Din the former case, the existence of the public firm is preferable as far as it earns non-negative profit, (2) in the latter case, given that at certain numbers of firms, MO deteriorates so-cial welfare, how the numbers are determined.
As a result, we prove that in such cases, the varidity of MO depends on demand, cost and the number of firms, and in relation to (1), non-negative profit of the public firm does not necessary indicate it.
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