Google revealed an important secret: the revenue shares for two AdSense services. Until now, publishers didn't know the percentage of the revenue that is paid by Google.
"AdSense for content publishers, who make up the vast majority of our AdSense publishers, earn a 68% revenue share worldwide. This means we pay 68% of the revenue that we collect from advertisers for AdSense for content ads that appear on your sites. (...) We pay our AdSense for search partners a 51% revenue share, worldwide, for the search ads that appear through their implementations."
It's interesting to note that the revenue share for AdSense for content has never changed since the service was launched, back in 2003.
Sevices like Google Search, AdWords and AdSense are usually treated as black boxes, since Google rarely reveals specific information about its algorithms.
Google AdSense's help center still says that "each AdSense publisher receives a percentage of the cost an advertiser pays for user clicks or impressions on their ad. This percentage is referred to as the revenue share. Google does not disclose the revenue share for AdSense."
Google's financial results for the first quarter of this year, show that only 30% of Google's total revenue is from partner sites and the traffic acquisition cost (TAC) is 26% of the revenue. "The majority of TAC is related to amounts ultimately paid to our AdSense partners, which totaled $1.45 billion in the first quarter of 2010." Google's partner sites generated revenues, through AdSense, of $2.04 billion. Obviously, 1.45/2.04~=0.71, which is very close to the AdSense for Content revenue share.