ges filed by competitors. Tariffing also facilitates oligopolistic behavior by making prices and service offerings both transparent and homogeneous. To the extent that retail access requires that all customers pay uniform rates for uniform services, it also limits network owners' ability to customize their offerings to the needs of particular customers and bars potentially welfare-enhancing forms of price discrimination. A complete analysis of the issues raised by price discrimination exceeds the scope of chapter.98 For our purposes, it suffices to point out that price discrimination can be particularly beneficial in industries like telecommunications, which involve large, up-front fixed costs. When fixed costs are SO large relative to the variable cost that the average cost curve lies above the marginal cost curve over the entire industry output, the prices charged to individual customers must cover a portion of the fixed cost as well as marginal cost. The fact that prices necessarily exceed marginal cost makes some degree of deadweight loss inevitable. Discriminatory pricing regimes, such as Ramsey pricing (1927), can take advantage of variations in different cus- tomers' price sensitivity to minimize those deadweight losses. Customers who are extremely price-sensitive (i.e., have highly elastic demands) are likely to curtail their consumption in response to a price increase to a greater degree than customers who are relatively price-insensitive (i.e., have fairly inelastic demands). Firms can thus minimize deadweight loss by allocating a smaller proportion of the fixed costs to price-sensitive customers and allocating a greater proportion of the fixed costs to price-insensitive customers. If fixed costs are allocated in inverse proportion to each consumer's elasticity of demand, price discrimination can lead to the efficient outcome. That said, retail access is not as disruptive as other forms of access. Because access is provided only to the network in its entirety at locations that the network already serves