realize all of available network economies. This does not mean that only one network will necessarily emerge and that government intervention is required to ensure that that network is the "right" one (Liebowitz and Margolis 1994). Even assuming for the sake of argument that circumstances permit network economic effects to give rise to the problems of monopolistic dominance and tech- nological lock-in, it is far from clear that other features of the market and the structure of consumer preferences might not mitigate, if not eliminate, these adverse effects. For example, the market may also dislodge an existing network technology SO long as the new network provides additional value that exceeds the value derived from the size of old network. 24 This is particularly true given that, after networks have captured a sufficient number of subscribers, the marginal benefit from adding another subscriber is likely to be low, which would greatly reduce the magnitude of any potential externality (de Fontenay and Lee 1983; Breslaw 1985; Mitchell and Vogelsang 1991; Yarrow 1996; Albon et al. 1997). In addition, network externalities may be substantially mitigated if user pref- erences are nonuniform. As Michael Katz and Carl Shapiro have noted, "Customer heterogeneity and product differentiation tend to limit tipping and sustain multiple networks. If the rival systems have distinct features sought by certain customers, two or more systems may be able to survive by catering to consumers who care more about product attributes than network size. Here, market equilibrium with multiple incompatible products reflects the social value of variety" (Katz and Shapiro 1994, p. 106; see also Liebowitz and Margolis 1996). The existence of large users may further mitigate any problems caused by net- work economic effects. If a single user controls a significant portion of the network, that user will be able to internalize more of the benefits of its adoption decision, 24 Katz and Shapiro (1994, p. 106) observe that new, incompatible standa