U.S. online advertising spending will rise to US$42 billion in 2013, up from $23.6 billion in 2008, according to November 2008 eMarketer data.

Search owns the biggest share, with 45.3 percent in 2008, and is expected to remain in the leading position, with 46.5 percent in 2013, SFN's World Digital Media Trends 2009 reported.Display ads accounted for nearly 20 percent in 2008, and are forecast to drop slightly to 19 percent in 2013. The classifieds sector, however, made up 13.3 percent in 2008, and is expected to see a drop in share to 7 percent in 2013, according to eMarketer.

Video ads are the biggest winner, expecting to account for 11 percent in 2013, up from just 2.5 percent in 2008.

Lead generation, sponsorship and e-mail are also likely to see a decline in share, according to the report, World Digital Media Trends 2009, released by SFN and the World Association of Newspapers and News Publishers.