A market system in which buyers bid against each other to reach the selling price of the security or instrument offered for sale. Through this system, buyers enter competitive bids and sellers enter competitive offers simultaneously. The price at which a stock is traded constitutes the highest price that a buyer is willing to pay and the lowest price that a seller is willing to receive. Some stock exchanges run live open outcry auctions on their floor. Participants in these auctions include a specialist, who acts as the auctioneer, floor brokers who execute orders on behalf of their clients, and registered traders who trade their own accounts. Some commodity and futures exchanges present live auctions.