This is made possible by Real-Time-Bidding technology that enables online display ads to be auctioned off in real time.

FORBES: See How Much You Are Worth To Online Advertisers

Forrester Research estimates that real-time bidding will constitute 18% of the online display-ad market this year, up from 13% last year.

WSJ: Online Tracking Increases, Fueled by Ad Auctions

Real-time bidding for online display is more efficient from a pricing standpoint, said Bob Arnold, Kellogg's associate director of digital strategy.

WSJ: Auction System Helps Place Digital Outdoor Ads