A method of processing bids over a network for an item to be sold, using a time based factor for an encountered level of demand, the method comprising, setting a first threshold level at which to offer the item at a first time, setting a second threshold level at which to offer the item at a second time subsequent to the first time, receiving one or more bids over the network, upon receipt of a bid, calculating a bid time as a function of the first threshold level, the second threshold level, the bid, the first time and the second time, and accepting bids received on the basis of the calculated bid time.