The breakdown, drawn from Nielsen's rating service, typically provides viewers' ages, gender, marital status and other personal data that help advertisers choose the audience most likely to be interested in their product or service.

New York-based Nielsen has been selling demographic data to television stations and advertisers for years.

Google's access to the information is significant because it gives the Mountain View-based company more tools to draw upon as it tries to target television ads as effectively as it has done on the Internet.

Because it processes more than 1 billion search requests per day, Google hasn't needed as much outside help to learn about the interests of its Internet users.

"This is another indication that Google is very serious about selling more ads in the mainstream media," said Brad Adgate, director of research for Horizon Media, which helps advertisers buy television ads.

Since May, Google has been delivering television ads for about 14 million subscribers to EchoStar Communication Corp.'s Dish network and Astound Broadband cable service.

The set-top boxes used by EchoStar and Astound enabled Google to track when commercials were watched and for how long. By drawing on Nielsen's data, Google will now have information on what kinds of viewers are watching the commercial.

"This was a missing piece of puzzle for us," said Keval Desai, Google's director of product management for TV ads.

Desai said Google is "thrilled" with its progress so far in TV advertising but declined to provide any financial specifics.

Even as it expands its ad platform into TV, radio and print, Google continues to make most of its money from text-based ad links posted next to search results and other online content.

Google's formula has been so profitable that it now has a market value of about $210 billion, second only to Microsoft Corp. in the high-tech industry.

The Google alliance appeals to Nielsen because the rating firm is trying to develop new measurement techniques and extend its reach into more digital media, such as iPods and mobile phones.

"The relationship with Google...is a prime example of the ways Nielsen is embracing new technologies, platforms and relationships worldwide to serve clients more completely," Nielsen Chairman David Calhoun said in a statement.