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)).