available profit simply by charging the monopoly price when the government limits the price it can charge for that input. Vertical integration into an unregulated market allows the monopolist to earn the profits denied to it in the regulated market by charging higher prices in the unregulated market (U.S. Department of Justice 1984, § 4.23). Such rate regulation, therefore, potentially gives monopoly producers the incentive to vertically integrate into an unregulated market and require all of their customers to purchase both products at prices that include the full monopoly markup. These incentives can be offset by competitive incentives to attract business in the unregulated market. A more subtle version of this argument applies when a firm subject to cost-of- service rate regulation provides an unregulated service that shares joint costs with the regulated service.37 In that case, it is alleged that the monopolist can attempt to allocate a disproportionate amount of the joint costs to the regulated service and recover those costs through its regulated rates, which is a real possibility given the inherent arbitrariness and uncertainty surrounding methodologies for allocating joint costs. Shifting a disproportionate amount of the joint costs onto the regulated market allows firms to reduce the size of the markup to cover joint costs included in the prices charged in the unregulated market. The firm's nonvertically integrated competitors, however, will have to charge prices that reflect the genuine allocation of the joint costs to the unregulated market. As a result, some commentators have argued that the essential facilities doctrine has greater potential relevance in the context of regulated industries. 38 Although the Bell Doctrine was once an important consideration with respect to telecommunications, economic and technological progress have undercut its Jefferson Parish, 466 U.S. at 36 (O'Connor, J., joined by Burger, C.J., and Powell and Rehnquist, JJ., concurring in judgment); Byars, 609 F.2d at 861. Jeffer