We examine a merger between two competitors in a Bertrand-Edgeworth model. We find that the effects of merger depend on the tightness of capacity constraints. The combination of two firms has no price effect if and only if the capacity constraints of all firms are binding both before and after the merger. However, a merger may turn a binding capacity constraint into a slack one, which results in higher prices. In an industry where excess capacity drives the premerger prices of all firms to the marginal cost, a merger may cause prices to rise even though aggregate capacity remains constant. (JEL L13, L40).