Auctions, which are applicable to aid-related procurement systems, have been recently recognized as an important tool for improving economic efficiency. Using data on procurement auctions for Japanese official development assistance projects, the equilibrium bid function is estimated. The data reveals that a 1% increase in the number of bidders decreases the equilibrium bid by about 0.2%. This implies that strengthening competition at procurement auctions lowers contract prices and mitigates the heavy indebtedness of developing countries. Auctions are also instrumental in fostering local business environment and governance. For intensifying bidding competition, it is useful to introduce an electronic bidding system, encourage local firms to jointly bid, and relax excessive qualification requirements. Copyright Springer 2006competition effects, official development assistance, procurement auctions, C31, D44, H57, L31,