We consider a vertically integrated input monopolist supplying to a differentiated downstream rival. With linear input pricing, at the margin the firm unambiguously wants the rival to expand — unlike standard oligopoly with no supply relationship — for either Cournot or Bertrand competition....

We consider differentiated duopolists facing symmetric linear demands and using Cobb-Douglas technologies with two inputs: a monopolized input and a competitively supplied input. Unlike with fixed-proportions technologies, a merger between the input monopolist and either firm can reduce welfare....

A vertical merger between a firm and an input supplier to that firm can generate efficiencies by eliminating double marginalization or alleviating other contracting inefficiencies. However, when the supplier also sells to that firm's rivals, a key antitrust concern is input foreclosure: the...