excess network capacity exists, the grant of a right of access does not foreclose any opportunities to sell space to other interested firms. The court concluded, then, that the opportunity cost of allowing another party to access the network was zero. Therefore, the court held that access rates need not include compensation for opportunity costs unless (1) the network was at full capacity and (2) other parties sought access, or the network owner had higher-valued use for that capacity. These opinions ignore certain aspects of networks' infrastructure investments that make excess capacity inevitable. Capacity in network industries is notoriously "lumpy" in that it can only be efficiently added in large, discrete quantities. In addition, if the needs of network users are to be met, such capacity must necessarily be added before it is actually needed, a problem that is particularly acute for carriers of last resort who are obligated to provide service to anyone who requests it. The tendency toward excess capacity is exacerbated further by the manner in which excess capacity can enhance network reliability and provide insurance against unforeseeable variability in demand. These qualities make excess capacity a feature that is endemic to all networks. In addition, these courts have fallen into the same trap as computer system managers that have allowed additional users free use of what, at the time, appeared to be excess capacity. That is, this approach overlooks the fact that use of what appears to be excess capacity imposes real costs by hastening the need for additional capacity. The fact that the use of the facility does not consume the facility is of no consequence. As we have pointed out earlier, this is a quality that is inherent in all physical networks and, to some extent, in capital assets generally. Finally, even assuming for the sake of argument that the costs associated with allowing access to a building were zero, it does not necessarily follow that nominal compensation is sufficient to make the building