Google and Yahoo have announced a two week experiment that will see the web giants take a share of each other’s advertising space.
During the trial Google will be able to put ads next to 3 per cent of search results on Yahoo.
Microsoft, which recently offered to buy Yahoo, has criticised the scheme.
“Any definitive agreement between Yahoo and Google would consolidate over 90 per cent of the search advertising market in Google’s hands. This would make the market far less competitive,” Brad Smith, Microsoft’s General Counsel, told the BBC.