Price cap regulation of a dominant firm facing competition

Price cap regulation is typically applied to natural monopolies operating with subadditive costs. Price caps are known to provide superior incentives for the regulated monopoly to pursue cost reduction and, in a multiservice/product context, undertake welfare enhancing price discrimination. It is well known that capping a Laspeyres index of the firm's prices induces the monopoly to charge socially optimal "Ramsey" prices in the long run. This paper examines the suitability of the Laspeyres form of regulation when the regulated firm faces competition in the market for one of its services (outputs). We present the appropriately modified Ramsey pricing rule for the regulated dominant firm and demonstrate that capping a Laspeyres index of the dominant firm's prices leads to prices that satisfy this pricing rule in the long run.