comScore has released the top 15 ad networks based on their reach among U.S. Internet users in December 2009.
The ranking found AOL Advertising remains the top ad network, reaching 187 million U.S. Internet users, or 91 percent of the total audience, followed by the Yahoo Network (180.9 million) and the Google Ad Network (178.1 million).
The fastest growing ad network by audience reach among the top 15 was Microsoft Media Network, which grew 31 percent compared to a year ago, followed by Collective Network (up 22%) and Audience Science (up 16%).
"Ad networks continue to be a powerful mechanism for delivering a large audience online, with eight different networks reaching at least 75 percent of the entire U.S. online population," said comScore senior vice president Jeff Hackett.
"Increasingly, however, ad networks are improving their capability for reaching more targeted audiences as well, which delivers enhanced value to advertisers and helps sustain higher CPMs for the channel. 2010 should bring us continued innovation and performance from this growing online sector."