We study the welfare effects of enabling peer supply through Airbnb in the accommodation industry. We present a model of competition between flexible and dedicated sellers (peer hosts and hotels) who provide differentiated products. We estimate this model using data from major US cities and quantify the welfare effects of Airbnb on travelers, hosts, and hotels. The welfare gains are concentrated in specific locations (New York) and times (New Year’s Eve) when hotel capacity is constrained. This occurs because peer hosts are responsive to market conditions, expand supply as hotels fill up, and keep hotel prices down as a result.

Auctions were very popular in the early days of internet commerce, but today online sellers mostly use posted prices. We model the choice between auctions and posted prices as a trade-off between competitive price discovery and convenience. Evidence from eBay fits the theory. We then show that the decline in auctions was not driven by compositional shifts in seller experience or items sold, but by changing seller incentives. We estimate the demand facing sellers and document falling sale probabilities and falling relative demand for auctions. Both favor posted prices; our estimates suggest the latter is more important for the auction decline. Survey evidence provides further support.