This paper tests the structure performance hypothesis by examining a highway construction industry in Florida. In the first-price sealed bid auction literature, there is little evidence on how many bidders are required for these markets to be competitive. Two different indicators are used to capture the transition from collusion to competition—a discontinuous effect of the number of bidders on winning bid price, and an associative effect of repeat bidding of a contractor with the same set of firms. The results suggest that winning bids decrease as the number of bidders rises until there are about six to eight firms. Since subsequent entry has no effect on the winning bid price, it is concluded that the highway construction market becomes competitive with about eight bidders.