This paper presents an exploratory analysis of the determinants of prices in online auctions for collectible United States one-cent coins at the eBay Web site. Starting with an initial data set of 20,000 auctions, we perform regression analysis on a restricted sample of 461 coins for which we obtained estimates of book value. We have three major findings. First, a seller's feedback ratings, reported by other eBay users, have a measurable effect on her auction prices. Negative feedback ratings have a much greater effect than positive feedback ratings do. Second, minimum bids and reserve prices have positive effects on the final auction price. In particular, minimum bids appear only to have a significant effect when they are binding on a single bidder, as predicted by theory. Third, when a seller chooses to have her auction last for a longer period of days, this significantly increases the auction price on average.

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This paper is an economist's guide to auctions on the Internet. It traces the development of online auctions since 1993, and presents data from a comprehensive study of 142 di¡erent Internet auction sites. The results describe the transaction volumes, the types of auction mechanisms used, the types of goods auctioned, and the business models employed at the various sites. These new electronic-commerce institutions raise interesting questions for the economic theory of auctions, such as predicting the types of goods to be sold at auction, examining the incentive e¡ects of varying auctioneer fee structures, and identifying the optimal auction formats for online sellers.

William Vickrey's predicted equivalences between first-price sealed-bid and Dutch auctions, and between second-price sealed-bid and English auctions, are tested using field experiments that auctioned off collectible trading cards over the Internet. The results indicate that the Dutch auction produces 30-percent higher revenues than the first-price auction format, a violation of the theoretical prediction and a reversal of previous laboratory results, and that the English and second-price formats produce roughly equivalent revenues. (JEL C93, D44)

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