Facebook is testing and will soon launch Facebook Exchange, a real-time bidding ad system where visitors to third-party websites are marked with a cookie, and can then be shown real-time bid ads related to their web browsing when they return to Facebook, Techcrunch.com reported.

This retargeting option could be a huge money maker for Facebook as it will allow for more relevant direct advertising.
 

For example a travel site could serve ads about a flight to Hawaii to someone who almost bought a flight on their site. Advertisers might pay big premiums for highly-accurate targeting. Users will be able to opt out of Facebook Exchange via third-party demand-side platforms, but they can’t opt out of the program completely from within the social network.

Facebook just notified TechCrunch that Exchange is currently in testing with eight advertising demand-side platforms, and it will become more widely available in the next few weeks for traditional Facebook sidebar ads charged at cost-per-thousand-impressions, but not Sponsored Stories or mobile.

The demand-side platforms currently testing Facebook Exchange, or FBX as some Facebook employees are calling it internally, are: TellApart, Triggit, Turn, DataXu, MediaMath, AppNexus, TheTradeDesk, and AdRoll.