There is disclosed a method for auctioning a set of keywords. Bids may be received from a plurality of advertisers. Each bid may include a value of a click-through and a budget expressed as a maximum number of click-throughs. A flow graph may be created that relates the set of keywords to the bids received from the plurality of advertisers. A minimum cost flow solution may be determined for the flow graph, and the keywords may be allocated to the advertisers based on the minimum cost flow solution.