This paper introduces an oligopoly model that includes three actors: a cartel (comprising two or more firms that operate like one merged company), a group of competing fringe firms, and a welfare maximizing antitrust authority. The cartel is the Stackelberg quantity leader and the fringe firms are in Cournot competition with respect to the residual demand. The cartel is internally stable if none of its member firms finds it profitable to become a fringe firm. The antitrust authority can destabilize the cartel in the sense of making the cartel internally instable. To this end, the antitrust authority has three policy instruments at its disposal: its own effort, a fine for detected cartels, and a leniency program for cartel members that cooperate with the authority. Taking into account that the use of these instruments is not costless for society, a unique optimal antitrust policy is derived. The analysis reveals that both, the optimal force and mix of the antitrust authority’s policy depend on market characteristics such as the efficiency of the authority’s operations, the public respect for the rule of law, the ethical standards of the firms’ managers, the market volume, and the number of firms operating on the market.

本文介绍了一种寡头垄断模型，该模型包括三个参与者：卡特尔（由两个或两个以上的公司像一个合并后的公司运作），一组竞争的边缘公司以及最大化福利的反托拉斯机构。卡特尔是Stackelberg数量的领导者，边缘公司在古诺（Cournot）的剩余需求方面竞争激烈。如果该卡特尔的成员公司都没有发现成为边缘公司有利可图，则该卡特尔内部稳定。从使卡特尔内部不稳定的意义上讲，反托拉斯机构可以破坏卡特尔的稳定。为此，反托拉斯机构拥有三项政策工具：它自己的努力，对发现的卡特尔的罚款，以及与该机构合作的卡特尔成员的宽大处理方案。考虑到使用这些工具对社会并非没有代价，得出独特的最佳反托拉斯政策。分析显示，反托拉斯机构的政策的最佳力量和组合取决于市场特征，例如机构的运作效率，公众对法治的尊重，企业管理者的道德标准，市场规模，以及在市场上运营的公司数量。