This program sets up a reverse auction in which the bidders are given roles that correspond to banks with portfolios of different mortgage-backed securities to sell. These securities can be retained or sold to the "government" at auction. The government has set aside funds to buy assets in order to inject liquidity into the system, and the banks are given liquidity goals. The "contracts" being sold pertain to different types of mortgage-backed securities. In order to enhance competition and reduce the required number of auctions, the government may structure auctions that cover a number of closely related securities. This inclusion of different securities in the same auction necessitates the use of some metric to compare bids to sell different securities. This metric is provided by "reference prices" that are estimated in advance on the basis of expert opinion and what market transactions there are. As the experimenter, you represent the government. You can specify the numbers of different securities involved, and whether a they will be combined in a single auction or sold in separate auctions. You also set the reference prices for each, and a budget amount to be spent. In a combined auction, submitted bids are ranked from low to high based on ratios of bids to reference prices, and bids with low ratios are included until the fixed budget is exhausted. All purchases are made at a common cutoff ratio, which when multiplied by the reference prices determine the payment to the seller. There are also two multi-round reverse auctions: a descending clock with supply function bids, and a multi-round uniform price auction in which the auctioneer announces which bids (offers to sell) would have been accepted had that been the final round, and bidders do not know in advance which will be the final round. The auctioneer (you) decide after each round whether to consider. Bidders may have either private "keep values," or they may be given signals concerning unobserved common values for each security.