This paper demonstrates that, in situations in which a cumulative exte
rnality exists, the basic nature and extent of resource misallocation
may be substantially less than we imagine. This conclusion stems from
deriving consistent conjectures In a unified framework in which conges
tion is present. Experiments support the conclusion that, when numbers
of agents are small, when there is little heterogeneity among them, a
nd when they have the opportunity to observe each other during repeate
d experiment, the market allocation may be efficient.