Upstream horizontal mergers involving a vertically integrated firm

We study upstream horizontal mergers when one of the merging parties is vertically integrated. Under observable contracting in the pre-merger case, we show that such type of mergers always harm consumers. However, under unobservable contracting in the pre-merger case, the input price may decrease and consumer surplus may increase as a result of the merger even in the absence of exogenous cost-synergies between merging firms. A necessary condition for this finding is that the unintegrated downstream firm is more cost-efficient than the downstream division of the integrated firm.