Worldwide social network advertising revenues will reach $5.54bn this year, according to eMarketer with just under half of that amount or $2.74bn coming from the US.

Social networking ad revenues will hit more than $8bn next year and almost $10bn in 2013 with around 52% of that coming from outside the US.

eMarkerer says that the bulk of these social network ad dollars will go to Facebook with a much smaller share will going to Twitter, which is estimated will hit $139m in ad revenues this year.

It predicts that ad revenues for LinkedIn will account for 3% of total worldwide social network ad revenues this year at $140.8m, which puts it on track to be bigger than Twitter, after it tripled its ad dollars in the last two years.

The report says that gains in social networking ad revenues mean that Facebook, Twiter and LinkedIn account for an ever greater share of all digital ad spending. In the US at the moment 8.8% of all online ad dollars go to social networking, 6.9% worldwide, and in two years time that figure will have jumped to 11.7% in the US and and 9.4% around the world.

eMarketer estimates of social network ad revenues are based on a “meta-analysis of estimates of consumer usage, marketer usage, ad pricing and impressions, as well as revenue estimates from research firms and other sources, and from interviews with industry executives”.