By David B. Wilkerson

CBS Corp. (CBS) said Tuesday it will participate in Comcast's trial of a new service that offers online content exclusively to the cable operator's customers.

Comcast Corp. (CMCSA) will soon begin a national technical trial of the service it calls "On Demand Online," carrying programming from Time Warner Inc.'s (TWX) TNT and TBS.

Comcast and Time Warner teamed up last month on a plan called "TV Everywhere," in a reaction to concerns that the wide availability of free, ad-supported television shows online through sites like Hulu, Veoh and others may one day lead many consumers to stop paying for video subscriptions - whether from cable, telephone or satellite providers.

The service will utilize an authentication system to verify that the user is a Comcast subscriber before allowing access to streaming content and, in the future, downloads to mobile devices.

CBS said it would make various types of current and library television shows available to Comcast's trial. A CBS spokeswoman said the specifics are "still being worked out."

CBS shows such as "CSI: Crime Scene Investigation" and "Survivor" are already available on-demand on television over Comcast's cable systems. The company also makes many of its shows of the past and present, such as "Ghost Whisperer" and "Hawaii Five-O," available at CBS.com and other online venues.

-David B. Wilkerson, 415-439-6400; AskNewswires@dowjones.com