Google launched a free hosted service on Thursday that helps Web site publishers sell advertising faster and fill unsold slots on their sites.

Ad Manager, which Google said has already been tested by a few businesses, is designed to streamline how ads are placed on Web sites and generate performance reports detailing how successful those ads are in reaching consumers, including click-through rates and revenue paid by the advertisers for those clicks.

Google said Ad Manager's purpose is to ease some of the problems that come with managing advertisements on a Web site, such as gauging available inventory and how to pick the highest-paying ads. The service is hosted on Google's servers, and Web site publishers can access it through a Web browser.

As of Thursday, Ad Manager entered a beta testing phase, and other publishers may apply to participate. Google makes technology such as Ad Manager available for free to enlarge the circle of publishers that use its advertising technology, bringing it revenue through fees.

Other online advertising specialist companies charge for similar placement and management services, including DoubleClick, which Google bought for $3.1 billion in April 2007. European regulators approved the acquisition earlier this week.

Ad Manager is flexible enough to let publishers sell their own advertising, Google said. For ad space they can't sell, publishers can opt to use Google's AdSense system to fill unsold slots.

Google's AdSense delivers text advertisements that are matched with the content of a Web site. Google will let publishers use Ad Manager in tandem with similar technology from other competing ad placement networks.

Ad Manager can also target ads at specific users. It is capable of delivering ads based on a user's domain, the brand of Web browser and language it uses, the PC's operating system, and how much bandwidth is available on their Internet connection.

That information may seen potentially sensitive, but it's automatically revealed when a browser visits a Web site. Increased attention has come around how Internet advertisers target ads to users and how they handle personal information.