• by Erik Sass  @eriksass1, December 7, 2011

The group of publishers launching private online ad exchanges is getting bigger, with this week’s addition of GateHouse Media, which owns hundreds of local daily and weekly newspapers around the country, along with their associated Web sites.

Access to the private exchange, powered by Casale Media’s real-time bidding technology and management platform, is restricted to a small group of agency trading desks and demand side platforms at launch.

The new Private Exchange is only open to buyers selected by GateHouse and Casale, allowing the publisher to ensure that only suitable brand advertisers gain access to its online inventory.

The list of DSPs with access to GateHouse’s Private Exchange includes MediaMath, which has worked with major brand advertisers like American Express, General Mills and Prudential. It is generally considered one of the largest DSPs operating today.

For its part, GateHouse offers advertisers extensive local reach. With 400 local newspaper Web sites in 21 states, including 79 dailies, GateHouse claims to reach a combined print and digital audience of 10 million people per month, generating 80 million page views per month via its local Web properties.

As noted, GateHouse is just the latest in a series of newspaper and magazine publishers to unveil private ad exchanges, which are usually intended to help move remnant online ad inventory while maintaining certain minimum price floors. This trend emerged in response to criticism that the established ad networks drive the price of online inventory down.

In February of this year, The New York Times Co., Gannett, Tribune, and Hearst launched a joint, private exchange managed by a joint venture called QuadrantOne, although The New York Times Web site itself didn’t participate.

 Gannett’s USA Today revealed plans to launch separate private ad exchange earlier this month. Conde Nast unveiled its own private ad exchange in mid-November, with access limited to a handful of major advertisers through the end of this year.