Two major factors to be considered in prequalifying construction contract bidders are the likely costs and risks to be faced by the client upon award of the contract. Prequalification of too many bidders, although lowering client costs, increases risks and causes an excessive overhead on the bidding process. A method of assessing the relative cost and risk implications associated with individual bidders is proposed. This involves calculating the percentage that bids are above the lowest bid in previous auctions, termed C-competitiveness. It is argued that selecting only the lowest and most consistent C-competitive bidders for a proposed contract auction will reduce client costs, risks and bidding overheads.