After months of speculation over its entry into the television advertising market, Google announced Monday evening that it would sell ads on the 125 channels of Echostar's satellite DISH Network.

Under the agreement, advertisers will bid on ad spots using Google's AdWords automated auction system. Google will analyze the anonymous data culled from the Dish network set-top boxes and only bill advertisers for the portion of the audience that watched a commercial a designated amount of time.

Advertisers can upload their TV commercials, bid on desired time and channel, and choose national area coverage. They can also choose to target by age demographic. The ads will be attached at the satellite operator level, not on the subscriber's set-top box.

The system is scheduled to start in May, and will sell ad space only on cable networks, including ESPN, CNN, Discovery, Lifetime, Nickelodeon and the Disney Channel. There are no national broadcast channels or local affiliates involved in the deal yet.

Television experts say the deal is a stepping stone to greater advertising control, but that Google really needs to sign an ad deal with one of the major cable networks, which are known for their ability to target ads sometimes as narrowly as neighborhood level.

Google is also reportedly planning to launch a marketplace that matches up marketers who don’t have experience creating ads with agencies that do.