Search marketing services firm Marchex said it has bought contextual ad network IndustryBrains for about $31 million in cash and stock, reports AdWeek. The deal brings to Marchex a network that powers paid listings on news sites such as USAToday.com, Businessweek Online, The Motley Fool and Forbes.com.

IndustryBrains advertisers choose which sites they appear on, whereas most contextual advertising networks require that advertisers run across various sites.

"The model basically asserts that there is value (and profit) in the voice and focus of an editorial site, as opposed to the un-variegated sweep of Overture and AdSense. This approach promises to raise the advertising revenues of niche sites which draw influential but smaller audiences," writes John Battelle in his blog (via paidcontent).

"This is a natural evolution in the paid search market," he adds.

"IndustryBrain's PPC pricing is above typical AdSense pricing, for good reason. They are delivering more qualified audience, which is the essence of what good publishing is about. The site even has a search tool that let's you see the cost per click in real time for any search term," Battelle concludes.

IndustryBrains also allows its publishers to sell their own advertising, writes AdWeek.

Marchex said it plans to sell IndustryBrains' advertisers search services and would use the IndustryBrains distribution network to get qualified leads for clients.

IndustryBrains will receive $15.6 million in cash and $15 million in stock, with $2.8 million of Marchex stock issued to IndustryBrains' employees who are joining Marchex.