Reston, Va.—U.S. Internet users were exposed to about 1.11 trillion display ad impressions in the first quarter of this year, with Facebook accounting for more than 346 billion of them, for a 31.2% share, according to a new report from digital marketing and online intelligence company comScore. This almost doubled Facebook's share from the same period a year ago, and was up from its 25.8% share of all digital ads served in the fourth quarter of 2010. Facebook is extending its display-ad lead over Yahoo sites, which in the first quarter delivered 112.5 billion display ad impressions, or 10.1% of the total, a bit higher than its 9.7% share the previous quarter. Top users of display ads for the quarter were AT&T Inc., with 19.5 billion impressions for the quarter, followed by Experian Interactive, Scottrade, Toyota Motor Corp. and Netflix Inc.