A method for balancing the allocation of available display slots on a Web page among a plurality of different sources of display items comprises (a) defining for each source a set of candidate items to be displayed, (b) selecting items from a pool of all candidate sets, in a manner that normalizes the probability that the items of any one candidate set will be selected in relation to the items of the other candidate sets, and (c) inserting the selected items into the available display slots of the Web page.