According to eMarketer, internet users prefer organic search listings to paid search ads, which suggests that SEO services may be more cost effective.
It cites data from the Search Engine Marketing Professional Organization which shows that $13.5 billion (£9.5 billion) was spent on search marketing last year.
Paid search ads accounted for 88 per cent of this spending, while SEO accounted for 11 per cent, the research reveals.
David Hallerman, a senior analyst at eMarketer, said he expects this trend to reverse somewhat in the future as advertisers come to realise that internet users find organic listings more relevant and are generally more accepting of them.
"SEO delivers longer-term results that support any search marketing campaign," he remarked.
Meanwhile, writing on the Econsultancy blog recently, tech reporter Patricio Robles said companies using SEO services should not confuse organic SEO with paid search marketing.