The world's biggest retailer, US-headquartered Wal-Mart, is hooked on TV.

The company, which shows consumer ads, movie trailers and corporate messages, among other offerings, on screens in nearly all its 2,600 stores, claims to be the fifth largest television network in the US and is now planning to upgrade the service.

Last year Nielsen Media Research found shoppers watched Wal-Mart TV an average of seven minutes per store visit, forty-four percent longer than in a similar study in 2002.

That growth has prompted an overhaul which will include around six hundred 42-inch screens in stores by the end of the year. The program will eventually roll out across the whole chain.

The company plans to tailor its broadcasts more specifically to areas of its stores and to individual stores, based on regional tastes and situations.

The increase in shoppers' viewing time has also attracted the attention of marketers searching for new ways to send their messages to increasingly elusive consumers.

Says Haston Lewis, vp for soft drinks and snack foods giant PepsiCo's Frito-Lay division: "From a marketing standpoint we want to be on the cutting edge of identifying and leveraging the most effective vehicles to capture consumers."

Household goods titan Unilever is also a dedicated Wal-Mart advertiser, and has created a campaign for its Dove brand using Wal-Mart workers as actors.

Data sourced from Wall Street Journal Online; additional content by WARC staff