Internet-enabled reverse auctions are commonly used in business procurement, but it's not clear how auction design affects buyer benefits. A study of over 700 online procurement auctions found that bidding competition, reserve price, and information sharing impact buyer surplus. Bid decrement and auction duration don't affect buyer benefits in this context. Using rank-bidding format can increase buyer surplus when current suppliers participate. These findings have important implications for future research and the design of online procurement auctions.