North American advertisers spent 44% more on search engine marketing last year than in 2004, with Google and Yahoo taking the lion’s share.
According to figures from the US-based Search Engine Marketing Professional Organization, advertisers spent $5.75bn (£3.4bn) last year on search engine marketing.
The organisation said it expected continued rapid growth, and estimated that the market would be worth $11bn by 2010.
The figures were reached on the basis of a survey of more than 550 companies conducted on behalf of the organisation by independent researchers.
Most of the spending was on paid placements, which accounted for 83% of the total. In addition, more cash was spent on optimising company websites to achieve better search rankings.
This optimisation accounted for 11% of spending. Paid search inclusions made up 4% of the total. Other marketing strategies made up the remaining total.