Since August 1990, land-scarce Singapore has held monthly public auctions to allocate Certificates of Entitlement (COE) or rights to vehicle ownership. Successful COE recipients pay the lowest successful bid in their vehicle category. This paper uses data envelopment analysis (DEA) to assess the relative technical efficiencies and the returns to scale of COE bidding in the five car categories. Technical efficiency measures the relative degree of minimization of COE premia against a weighted array of demand, price and economic factors proxying market conditions at each monthly exercise or decision-making unit (DMU). COE bidding is shown to be relatively efficient contrary to the belief that the 'single-strike-price' auction mechanism encourages overbidding. The influences of several policy measures and economic conditions on the COE premia are also discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.