This year, the market for online display advertising - including interactive video ads that run in a fixed place on a page - could reach $5.5 billion, estimates David Hallerman, a senior analyst at eMarketer. That's less than the market for text ads related to searches, which is expected to bring in about $8.2 billion this year. Compare that with 2000, when search ads accounted for just 1.3% of the total online ad market, while display ads brought in 47%, says Hallerman. As companies such as Google were able to make the ads highly targeted, providing marketers with clear returns, search ads became more expensive, eventually dominating the field.

Ad-exchange services such as Right Media want to do to display what Google did to search. Exchanges increase the price of ads by letting advertising networks that track Web surfing behavior buy space, in front of users they recognize, on nonpremium Web pages?pages with content that an advertiser doesn't specifically want to be associated with, such as Yahoo Mail pages. The networks can afford to pay more for these pages because they are delivering even higher priced ads thanks to their tracking information. "By allowing other publishers access to our inventory?we will ultimately achieve premium pricing from both of those elements," said Susan Decker, Yahoo's chief financial officer, on a conference call following the announcement.

Since acquiring a 20% stake in Right Media for $45 million in October, Yahoo has seen a 50% increase in the price of ads on the so-called nonpremium pages it has made available through Right Media. Other Web publishers have seen their ad prices increase, too.

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