• by Gavin O'Malley  @mp_gavin, May 10, 2010

Yahoo's share of the ad-serving market shrank to 4.39% from 9.7% at the end of 2008, according to a report from Attributor, a provider of content monitoring and monetization platforms. While Yahoo ranks ahead of MSN and ValueClick, it has fallen behind AOL, which has 7.15% of the market, along with Revenue Science with a 6.83% share.

Google and DoubleClick, meanwhile, continued to dominate the market with a combined 65% share, according to Attributor.

Compared to Attributor's most recent report conducted in December 2008, the combined share of Google and DoubleClick has further increased by about 9%. By contrast, Yahoo's share decreased by more than 5% -- or half of its previous share.

Between Google and DoubleClick, Google dominates the smaller sites -- less than 1 million views -- whereas its market share is about the same on the larger sites -- more than 1 million views).

According to Attributor's report, AOL's market share increased partly due to its acquisition of Adtech, which it considers to be quite strong on European Web sites, including Sky Network sites like Sky.com and SkySports.com.

AudienceScience is strong on news sites like CNN.com, USAToday.com, and WashingtonPost.com. In fact, on these news sites, AudienceScience is ahead of both Google and DoubleClick taken separately.

With regard to market share for large sites -- greater than 1 million unique users -- DoubleClick and Google dominate, and about equal size. AOL and AudienceScience both ranked ahead of both MSN and Yahoo.

Meanwhile, in market share for small sites -- less than 1 million unique users -- Google dominated by capturing about 50% of the entire market, and combined with DoubleClick, captures more than 70% of the market. Similarly, MSN and Yahoo now rank behind AOL, AudienceScience, ValueClick and Kontera.

For the report, Attributor processed 270 million pages -- compared to 75 million in late 2008 -- as a result of greater capacity and a longer collection period. There were 37 ad networks that could be identified. The data was then combined with Compete.com's traffic data and its vertical site category classification to provide the unique user and content category breakdowns.

Attributor licenses content and reader analysis technology to publisher clients, including Reuters, Condé Nast, and the Financial Times.

The Redwood City-based firm fingerprints and continuously monitors its clients' original content as it is distributed across the Web -- providing analysis, statistics and a clear view of how the content is being discussed, re-used, and monetized.