This paper investigates conditions that generate the so-called "waterbed" effect under price regulation. This is the effect whereby regulation of one price of a multiproduct firm causes one or more of its unregulated prices to change as a result of the firm's profit-maximizing behavior. A waterbed effect is shown to arise when demands and/or marginal costs are interdependent, firms use nonlinear pricing, or there is a zero-profit constraint or global price cap. Some implications for market definition, welfare analysis of regulation, non-price competition, collusion and two-sided markets are also discussed, as well as specific applications to fixed-to-mobile termination and bank overcharges.
The "Waterbed" Effect and Price Regulation