The author determines the endogenous degree of vertical integration in a model of successive oligopoly that captures both efficiency gains and strategic effects. Foreclosure effects are purposely left aside. The profitability of integration originates in the greater ability of integrated firms to adopt a specific type of technologies. The author shows that vertical merger waves can stop by themselves before integration is incomplete because of strategic substituability in vertical integration. This is in contrast to the strategic complementarity result in McLaren [2000] that leads to either incomplete integration or complete separation.