US broadcasting corporation CBS has agreed to purchase web publisher CNET Networks for $1.8bn.

The deal will make CBS one of the top 10 web publishers in the world, giving the company a total of 54 million unique visitors per month. The company estimates that its sites will reach 82 per cent of all US web users.

In addition to its CNET and News.com sites, CNET also runs gaming site GameSpot, music site MP3.com and shopping site MySimon. Other sites in the company's network include TechRepublic, Download.com and UrbanBaby.

On closure of the deal, CBS plans to integrate CNET's network of sites into its existing internet operations under the CBS Interactive brand.

"The core businesses of CNET Networks and CBS Interactive represent near perfect category symmetry in premium online content," said Quincy Smith, president of CBS Interactive.

"Together we will have a terrific opportunity to grow our established businesses and build new attractive verticals of content. This is the beginning of an era for CBS and CNET Networks.

CBS expects the deal to be finalised by the autumn.