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This study examines the optimal taxation in a free-entry Cournot oligopoly using the average cost function and aggregative games approach when either a specific tax, an ad valorem tax, or both, is imposed. When either a specific or an ad valorem tax is imposed, we obtain the following results. First, the business-stealing (business-augmenting) effect in the free-entry equilibrium makes the optimal tax rate positive (negative). Second, social welfare under the optimal specific tax is lower than that under the optimal ad valorem tax. Third, when both taxes are imposed, marginally increasing a positive ad valorem tax (negative specific tax) improves social welfare when the optimal specific (ad valorem) tax is initially imposed. Finally, the optimal combination of a specific subsidy and ad valorem tax depends on the shape of the average cost function.Résumé. Taxation optimale dans un oligopole de Cournot à libre entrée : l'approche de la fonction du coût moyen. Cette étude examine la taxation optimale dans un oligopole de Cournot à libre entrée en se servant de l'approche de la fonction du coût moyen et des jeux agrégatifs lorsqu'une taxe spécifique, une taxe ad valorem ou les deux sont imposées. Lorsqu'une taxe spécifique ou ad valorem est imposée, nous obtenons les résultats suivants. Premièrement, l'effet de vol de commerce (augmentation de commerce) dans l'équilibre de libre entrée rend positif (négatif) le taux d'imposition optimal. Deuxièmement, le bien-être social est plus faible avec la taxe spécifique optimale qu'avec la taxe ad valorem optimale. Troisièmement, lorsque les deux taxes sont imposées, la mise en place d'une taxe marginale ad valorem positive (taxe spécifique négative) améliore le bien-être social lorsque la taxe spécifique (ad valorem) optimale est imposée au départ.

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This article theoretically investigates how different ownership structures of patents affect ex ante and ex post incentives for innovation by applying a property rights approach. We explore a model in which two research laboratories invest in R&D to obtain an innovative patent, and after successfully obtaining the patent they determine an ownership structure for the patent. The two parties consider how the determined patent ownership would affect their noncontractible relation-specific investments for commercialisation. We demonstrate that joint ownership of a patent between two parties is optimal. More concretely, if a selfish (altruistic) relation-specific investment is more important than an altruistic (selfish) investment, a joint ownership with no (bilateral) veto is optimal to maximise the joint value. Moreover, when both parties do not commit themselves to joint ownership in advance, they have greater incentive to invest in R&D than committing, even if they understand that joint ownership is desirable ex post.

This paper revisits De Fraja and Delbono (1989), which is the seminal paper on mixed oligopoly, in order to pay more attention to Stackelberg competition. First, we show that, even in Cournot competition, if the number of private firms is sufficiently small, privatization necessarily reduces social welfare. Second, we demonstrate that when a public firm is a Stackelberg leader before and after privatization, privatization necessarily reduces welfare irrespective of the number of private firms. Moreover, we show that even when a public firm remains a follower, privatization reduces welfare if the number of private firms is relatively small.