Abstract: A method of allocating advertising space. Information about a user that is currently accessing the web page is provided to a number of advertiser computational agents, along with statistical data on the relative value of the particular ad placement. These agents compute for an advertiser, the advertiser's “effective Return On Investment” (eROI) for showing an ad impression to this user. eROI prices are received from the eROI agents within an interval after the user is identified and the space is allocated. A publisher computes a “Customer Relevancy Score” (“CRS”), taking into account whether the user will exit if the ad is clicked on (retention), user satisfaction (relevance, context), and content rating (exclusions). Finally, the “Publishers Ad Score” (“PAS”) is computed for the visit, fully reflecting both the advertisers evaluation of the opportunity, and the publisher's interests.