Facebook served up the greatest number of online display ads among all online publishers tracked by ComScore over the third quarter.

With a total of 297 billion online display ads, the popular social network accounted for 23 percent of all ad impressions (the number of times an ad is displayed), ComScore announced yesterday. Facebook's market share for ad impressions jumped 13.9 percentage points from 9.2 percent in last year's third quarter.

Yahoo came in second for the quarter with 140 billion display ad impressions, followed by Microsoft with 64 billion, and Fox Interactive Media with 48 billion. Display ads specifically include static and rich media ads but exclude video ads, house ads, and very small ads, according to ComScore.

Among online advertisers, AT&'T was at the top of the rankings with 21.1 billion ad impressions, 1.6 percent of all display ads tracked by ComScore. Online trading firm Scottrade was second with 14.9 billion impressions, followed by Verizon with 14.6 billion. For the quarter, 109 different advertisers delivered at least 1 billion display ad impressions, a solid rise from from 76 last year.

Overall, the online display ad market showed a healthy rebound from last year's soft environment. Almost 1.3 trillion display ads were delivered to U.S. Internet users in the third quarter, a 22 percent jump from a year ago.

"Just one year ago we were still in the midst of an advertising recession, but several growth drivers have contributed to sustained improvements over the past few quarters," comScore senior vice president Jeff Hackett said in a statement. "The ability to buy specific audiences is enabling a greater number of display ads to be delivered on target, display formats are improving at a rapid rate, and the quality of creative is getting better every day. As publishers prove the value of online display ad campaigns, digital should continue to carve out a bigger piece of the advertising pie."

On the receiving end of all this online ad activity, the average U.S. Internet user was hit by more than 6,000 display ads over the course of the quarter, according to ComScore.