中文摘要：

横向并购可能给参与并购的企业带来成本节约而产生效率效应，同时也可能产生反竞争效应。在横向并购反垄断审查的效率抗辩中，并购企业只要能够证实成本节约的效率效应能够抵消反竞争效应进而增进社会总福利水平，就可以获得反垄断当局的批准。然而，成本节约及其实现程度具有不确定性，成本节约的不确定性不仅会影响消费者剩余和社会总福利水平，而且将对效率抗辩和反垄断当局并购审查的判定规则产生影响。本文以Coumot模型为基础，系统分析了成本节约的不确定性对于横向并购反垄断评估审查中效率抗辨、判定规则和预期消费者福利的影响，为反垄断当局在并购评估审查中如何考虑效率因素提供决策参考。

英文摘要：

Merger can bring the efficiency gains by create cost savings for the merging firms. If the merging firms could confirm that the efficiency effects can offset the anticompetitive effects and enhance the total social welfare, the antitrust authorities will approve the merger. However, the efficiency and the degree of realization are uncertainty. This uncertainty will not only influence the consumer surplus and total social welfare, but also influence the efficiency defense and the decision rules in merger control. The paper analyzed the influences based the Cournot model and provided some references for the antitrust authorities in the merger assessment.