Google Leads in Ad-Serving Share

Microsoft's Atlas Trails Yahoo, AOL

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NEW YORK ( -- Google is not only a juggernaut in search, it also has a significant -- although declining -- share of the ad-serving market, according to a study from Attributor, a content-tracking firm.

DoubleClick and AdSense are responsible for more than half of all online-ad-server calls, or 31% and 26% respectively, Attributor reported. The next closest was Yahoo, at 10%, followed by AOL and Revenue Science, both at 7%. Surprisingly, Microsoft, which owns the Atlas ad-serving system, had only 4% of the market.

Ad Server Market Share

Attributor scans billions of web pages to find out where and how content is being used so publishers can request licensing agreements, links or shares of ad revenue. In its October 2008 crawling operation, it also analyzed server calls across 75 million domains. A server call is the moment when a website requests an ad to serve up to a user. The study examined whose ad code was on that page.

Why Google's share is so large
One reason Google notches so highly in this particular study is that it includes both display and text ads. Additionally, in counting the number of ad calls, text ads and display ads are treated equally. However, it should be noted that on any given website, a publisher often displays three text ads where it would have room for one display ad.

Share figures for DoubleClick and AdSense were down 3% and 9%, respectively, from last January, the most recent month Attributor conducted the research. Additionally, Google's AdSense appears to be moving toward servicing more large publishers. It gained two share points on larger sites compared with January's data but lost 13 share points on smaller sites.

Ad Server Market Share Breakdown by Site Traffic chart

One way to look at the data, said Rich Pearson, VP-marketing for Attributor, is to see who has gained share since January, which would suggest they are doing a better job monetizing content. AOL gained 1.5 points of share, which may have to do with more aggressive rollout of its AdTech ad serving technology. ValueClick and AdBrite also gained share.

Microsoft's low share surprising
When asked about Microsoft, Mr. Pearson said it was indeed surprising that it didn't command more market share, but noted that it had a similarly low market share in the January study, which perhaps speaks to its need to partner with Yahoo.

The study also broke down server share by vertical segments. While Yahoo had 10% market share generally, it had 14% in the health category. And DoubleClick had 31% overall but 58% in the automotive category.

It's important to note that Attributor's figures don't represent the share of publishers each ad server works with; rather the company counted up all the ad-server calls across 75 million domains and then applied unique user numbers to those domains (using data). As Mr. Pearson said, that makes sure an ad-server call found on Yahoo counts a lot more than one on For example, if has an ad code with, Attributor counts that as Atlas and then queries for the number of visitors to the page in October to come up with share totals.

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