The model incorporates an infinite series of auctions for identical items (or close substitutes) ordered over time and bidders with unit demand. The participants of each auction are drawn from a dynamic pool, with losing bidders remaining in the pool of potential bidders. The number of bidders in each auction is unobservable. Risk-neutral, forward-looking bidders submit bids below valuation. A novel identification and estimation strategy is used to estimate the valuation distribution from an order statistic of the bids. The model is used to evaluate the efficiency of online auctions for a 60GB Apple iPod Video, compared to a perfect-competition benchmark.