Forrester predicts online advertising billings to reach $14.7 billion in 2005, up 23 percent from last year, according to BtoB Online. The firm predicts that online advertising will account for 8 percent of all ad spending by the end of 2010, and that search engine advertising will soon overtake display advertising spending on the internet.

Forrester expects search marketing to grow 33 percent this year, eventually growing to $11 billion by sometime in 2010. The firm expects display advertising to grow about 11 percent per year between now and then, reaching $8 billion. Forrester surveyed 99 of the biggest spending marketers to help make its predictions.

On Monday, eMarketer predicted 2005 billings would reach only $13 billion, which it said would be a 34 percent increase from 2004. It also predicts continued stronger growth for search marketing billings.