Abstract: A method of determining the placement of a plurality of different Internet advertisements at a plurality of different Internet publisher websites sites each having an advertisement placement space. For each user visiting a publisher website, an impression of an advertisement is served. Initial web browsing activity data is recorded for each impression served. Subsequent action data associated with the service of the impression is recorded. The subsequent action data is associated with the initial web browsing activity data to generate an effectiveness level for the combinations of advertisements and placement spaces. Based on the generated effectiveness levels, serving of the advertisements is distributed among the placement spaces.