Facebook accounted for over 16 percent of all ads served to U.S. users during the first quarter of 2010, making it the largest online display ad publisher in the country, according to data from comScore.

The online measurement firm estimates the social network displayed 176 million impressions during the first three months of the year. That's considerably more than the 132 million impressions estimated on Yahoo-owned properties, the second largest publisher in ad terms with 12.1 percent of all online ads during the quarter.

Facebook's ad impressions have therefore grown by 52 percent versus Q4 2009, when it served around 115 million impressions. In the same period impressions on Yahoo sites dropped from 140 million to 132 million, and impressions on Microsoft, Fox Interactive Media, and AOL properties also dipped, quarter-over-quarter.

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