Facebook ad revenue comes from surprising segment

As Facebook soars in popularity, its ad revenue is growing quickly. But where that money is coming from may come as a surprise. Of the $310 million Facebook will make in revenue this year, 74 percent ($229 million) will come from local advertisers, according to a report from Borrell Associates.

Marketers are expected to spend $3.3 billion on social networks this year, according to Borrell's estimates, and 20 percent of that will come from local advertisers. That's roughly $641 million, but what's more amazing is that more than half of that amount will be spent on the top two social networks: Facebook and MySpace.

MySpace, which is now second to Facebook in traffic, still brings in the most ad revenue of any social network, and will make more than $500 million this year, according to Borrell. Roughly 26 percent of its ad revenue comes from local.