• by Mark Walsh  @markfwal, March 26, 2013

Facebook on Tuesday said it had begun testing ads sold through the Facebook Ad Exchange (FBX) in the news feed. Until now, those ads -- which allow marketers to retarget Facebook users based on their browsing habits across the Web -- have appeared only on the right side of pages.

The change will allow advertisers to run Page Post ads in both the right rail and the news feed on the desktop. (FBX doesn’t extend to mobile retargeting yet.) The ads, geared toward direct-response advertisers, will link back to the landing pages of sites a user has visited. The ads will appear the same as existing Page Post ads in the news feed.

For the test, Facebook is working with a trio of demand-side platforms already approved for FBX: MediaMath, Nanigans and TellApart. It will start making the ads available to more DSPs and advertisers in the coming weeks.

Since introducing ads into the news feed last year, Facebook has touted higher interaction rates for these “native” formats than ads appearing in the right column. During the company’s fourth-quarter conference call in January, CFO David Ebersman said news feed ads drive eight times more offline sales than right-rail ads on the site.

About 65% of Facebook marketers were advertising in the news feed at the end of 2012, up from 50% in the fourth quarter. With the addition of FBX ads, that figure is likely to continue rising. Since formally launching its FBX retargeting platform last fall, Facebook and its ad partners have also reported positive results from campaigns.

One lingering question around news feed ads, however, is whether Facebook could end up alienating users if it overloads their feeds with Sponsored Stories, Pages Posts or other formats. The company believes the number of ads in the news feed won’t increase as a result of the inclusion of FBX ads, according to the Inside Facebook blog.