本文運用連續Cournot寡占模型分析垂直相關市場中，垂直整合廠商的存在如何影響下游競爭廠商利用觸發策略形成暗默勾結的可能性。結果顯示，郵直整合廠商策略性買入中間財的行為會使下游競爭廠商之間的勾結變得更加困難。因為策略性買入的效果會隨下游競爭程度的上升而減弱，所以當下游競爭廠商勾結時，中間財價何會因垂直整合廠商買入較多而上升，從而降低廠商勾結的獲利；當下游競爭廠商回歸Nash均衡以懲罰背離廠商時，中間財價格隨垂直整合廠商減少策略性買入而相對下降，使得背離廠商面對的懲罰較不嚴厲。

This paper employs a successive Cournot oligopoly model to investigate the impact of vertical integration on the sustainability of downstream tacit collusion. We find that the strategic buying by a vertically integrated firm in the intermediate good market can make tacit collusion harder to sustain. The reason is that the effectiveness of strategic buying is inversely related to the degree of competition in the downstream market. Therefore, in the collusion phase, the integrated firm disadvantages the downstream cartel with a higher intermediate good price by buying more intermediate goods strategically. On the other hand, in the phase of Nash reversion, the punishment for deviation is ameliorated by a lower intermediate good price as a consequence of reduced strategic buying.