ºÃÉ«App

The combinatorial clock auction is becoming increasingly popular for large-scale spectrum awards and other uses, replacing more traditional ascending or clock auctions. We describe some surprising properties of the auction, including a wide range of ex post equilibria with demand expansion, demand reduction and predation. These outcomes arise because of the way the auction separates allocation and pricing, so that bidders are asked to make decisions that cannot possibly affect their own auction outcome. Our results obtain in a standard homogenous good setting where bidders have well-behaved linear demand curves, and suggest some practical difficulties with dynamic implementations of the Vickrey auction.