Google began allowing publishers to purchase ads on specific sites on its AdSense content network in April 2005. But currently, when advertisers buy ads across the entire network, they are not told the number of sites their ads appear on or which sites they are--merely how many clicks they received.
Josh Stylman, a managing partner with search engine marketing firm Reprise Media, said that lack of transparency is relatively common for the search giant.
"Transparency is a problem for anyone who does business with Google on any level--whether you're an advertiser, a publisher, a member of the press or a member of the financial community," he said.
When the new feature is fully implemented, an advertiser's standard report will carry a list of sites where a spot appeared, according to a Google spokesperson. The feature is currently in early beta testing, and is scheduled to launch in the second quarter of this year.
The move could help advertisers who have avoided using the network for fear their ads would appear next to objectionable content.
A report in The New York Times suggested that the move came in response from growing market share gained by contextual advertising firm Quigo, but a spokesman for Google denied the connection.
Stylman said it's unlikely that Google would change its strategy based on a smaller competitor's system, but that Quigo's approach was gaining significant share in the market.
"I don't think that Quigo is a significant enough player for them to change their entire system based on them," he said. "Having said that, Google's intelligent enough to keep an eye on market trends, and Quigo is definitely gaining some market traction."
Quigo last week announced a multi-year partnership with Forbes to serve contextually targeted ads on its sites including Forbes.com, ForbesAuto.com and ForbesTraveler.com.