The Google ad serving juggernaut appears secure even if Microsoft and Yahoo agree on a deal to merge their search advertising businesses.   Our analysis of ad server calls across 75 million domains shows that both Yahoo and Microsoft lost significant share compared to our March report and now make up less than 15% of the total market.

The explosion of new ad networks in 2008 had an impact, but only one newcomer  – Revenue Science- broke into the top 5.   Unsurprisingly, Google’s AdSense is dominant on smaller sites while Google-owned DoubleClick leads on larger sites; however AdSense made great strides on larger sites, leapfrogging Yahoo into 2nd place.

Read on for more details including new breakouts by content category. If you are a publisher looking to tap into the viral syndication of your content, please contact us for a free report on how your content is monetized across the Web.

Key Findings

• DoubleClick and AdSense  continue to dominate ad server market share, capturing 31% and 26% of Unique Users, respectively.

• DoubleClick continues to own the “Head” while AdSense owns the “Tail”.

• For larger sites with over 1MM Monthly Unique Users, DoubleClick has a 36% share, a nearly 3x share advantage over its nearest non-Google competitor, Yahoo. Together, AdSense and DoubleClick capture 54% of this segment.

• For smaller sites with less than 1MM Monthly Unique Users, AdSense has a 38% share, a more than 7x share advantage over its nearest competitor, ValueClick.  Together, Google and DoubleClick capture 60% of this segment.

• Share positions for the ‘Big 3’ – DoubleClick, AdSense and Yahoo – vary widely by vertical.

• DoubleClick share is strongest on Automotive sites (58%), whereas AdSense rules Blog sites (40%).  Yahoo is strongest on Health sites (13%).

• AdSense has gained  2 points of share on large sites while Yahoo has lost 4 points since the March report.

Overall Ad Server Market Share

Ad Server Market Share Breakdown by Site Traffic

Ad Server Market Share Breakdown for Selected Content Categories

Methodology

Attributor analyzed the ad server calls across 75 Million domains as part of its October 2008 crawling operations.  For a refresher on the difference between an Ad Server and Ad Network, there is a good description here .   The data was then combined with compete.com’s October 2008 traffic data and its vertical site category classification to provide the unique user and content category breakdowns.   Each share total represents the sum of all ad networks owned by each company, with Google as the exception in which DoubleClick and AdSense are displayed separately.  For example, Atlas DMT share is counted within Microsoft share numbers and Advertising.com is included in AOL share numbers.

*** Update 12/19/08 ***

After speaking with the folks at OpenX, a popular free ad server for publishers,  we discovered that we were not detecting their share correctly.  We are working with them to fix for our next release.