Citing an oncoming economic slowdown, eMarketer has lowered its forecast for online ad growth in 2006.

eMarketer's annual report on ad spend lowers its forecast for online from $16.7 billion to $15.9 billion in 2006, and predicts a slowing annual growth rate of 26.8 percent, down from recent years' 30-percent-plus growth rates, reports AdAge. Nevertheless, ad spend is expected to remain relatively robust. Online Publishers Association members, for example, are expecting third-quarter revenues to be greater than they anticipated in the first quarter.

Moreover, eMarketer expects U.S. online ad spend to reach $21 billion in two years and surpass $25 billion in 2010 - and growing from 5.7 percent of total ad spend in 2006 to 8.9 percent in 2010. Paid search is expected to constitute the majority of online ad spend, accounting for more than 40 percent through 2010.

However, as major advertisers jump aboard the internet advertising bandwagon, the online-advertising share of rich media, including video, is expected to grow from 9.0 percent in 2006 to 18.0 percent in 2010, while display ad share falls from 21.0 percent to 17.8 percent.