Policy debates about natural resource auctions continue to arise
(e.g. oil, timber), and the subtleties of procurement auctions have led to interesting theoretical extensions of standard models and new questions that can be asked of bidding data (e.g., Athey and Levin (2001), Bajari, Houghton, and Tadelis (2004), Asker and Cantillon (2004), Asker and Cantillon (2005)). The choice of auction design for treasury bills has changed in recent years, partly in response to academic arguments, although the issue is far from settled. Recent applications of multi-unit auctions to allocate goods (e.g., radio spectrum) that may be substitutes or complements have inspired new theory, experimental work, and empirical work (e.g., Cantillon and Pesendorfer (2003)).