Online advertising revenue reached 6.1 Billion U.S. dollars in the fourth quarter, an increase of 2.6 percent over the same period last year, according to a report (pdf) by the Interactive Advertising Bureau and PricewaterhouseCoopers. Fourth quarter revenue was 4.5 percent higher than the third quarter of 2008. Revenue for 2008 reached 23.4 Billion U.S. dollars, an increase of 10.6 percent over 2007. Search advertising revenue show the largest increase of any format, an increase 20 percent to 10.5 billion dollars in 2008. Display advertising revenue, which includes display banner ads, rich media, digital video, and sponsorship, increased nearly 8 percent to 7.6 billion dollars. Classifieds revenue decreased 4 percent to 3.2 billion dollars, referrals/lead generation revenue increased 6 percent to 1.7 billion dollars, and e-mail revenue decreased 4.5 percent to .4 billion dollars. Performance based advertising accounted for 57 percent of revenue, with cost per thousand (CPM) accounting for 39 percent and hybrids accounting for 4 percent.