Behavioral targeting involves following a visitor to a high-demand area through cookies and serving ads to them in other content. Before spinning off unsold inventory to the networks, many of the bigger sites use an auction model for large DR advertisers. The auction model permits the portals and other majors to get the highest rate possible for inventory after the natural demand has been worked through. Network distribution is the most common method of selling off unwanted impressions.

Those that tout behavioral targeting regard it as the panacea for all inventory issues. The rationale is that any impression against a valued consumer who is "in market" for a specific product or service as indicated by specific content viewing can be effective. In fact, recent research for Tacoda from Bill Harvey, CEO of TRA, Inc. suggests that the surprise factor of finding an ad served through behavior technology -- but to the right demographic target outside of a contextual placement -- works better than contextual ad after the first impression. AOL research showed that its subscribers accepted the concept of behavioral targeting. This type of targeting is used extensively by many sites through the services of companies like Tacoda, Revenue Science and others. Yahoo was an industry leader in developing behavioral targeting early. In fact, this is now a key strategy for their inventory control.

The numbers suggest that if behavioral targeting were to be accepted on a universal basis, the amount of available inventory that is regarded as preferred could grow substantially, easing inventory issues.