By Deborah Yeo,AP Business Writer

PHILADELPHIA-Comcast Corp., CBS Corp. and General Motors Corp. are testing a new concept in video on demand: Prime-time TV shows free for digital cable subscribers.

Starting Monday, cable viewers in Philadelphia, Baltimore, Chicago and Detroit will be able to watch “Survivor Finale” and “Survivor Reunion” at no charge because GM will be the sole sponsor. The shows will appear on video on demand a day after they air over broadcast TV, and run until Aug. 31.

There will be commercials at the start, middle and end of the shows.

The shows will appear in markets where CBS owns and operates TV stations, since affiliates take a dim view of the network providing shows through other outlets in their areas.

Video on demand lets digital subscribers watch archived shows and movies at any time.

The announcement extends Comcast’s relationship with New York-based CBS. Earlier this year, the network offered prime-time shows such as “Amazing Race,” and “CSI: Crime Scene Investigation” through Comcast’s video-on-demand network for 99 cents each.

While the test market is small, the stakes are high: Comcast and other cable operators are banking on video-on-demand services to keep subscribers from jumping to satellite TV, which doesn’t have this capability. But VOD’s problem is that newer shows cost money and free shows are older.

Charlie Thurston, president of Comcast Spotlight, said in a statement that the cable operator wants to further develop video-on-demand programs supported by advertisers.

“We are committed to developing VOD as an ad-supported platform,” he said.

Comcast, based in Philadelphia, is the nation’s largest cable operator.

AP-ES-05-12-06 1642EDT