Abstract: A data processing procedure is shown in which the processed data includes data representing negotiations for the purchasing of a package of inventory, taking the form of offers and counter offers between a single major party and a plurality of minor parties, and data stored in a database representing details of the items of inventory available for sale. The procedure identifies a package of inventory from the database and presents a major graphical user interface to a major party that shows data from each of a plurality of participating minor parties. Minor graphical interfaces are presented to each of the minor parties that show a first indication of time remaining (601) a second indication of the proportion of the package of inventory remaining (602) and a representation (603, 604, 605) of each participating minor party.