Google, Microsoft and Yahoo are all vying for the right to post their keyword advertising in front of Ebay’s millions of online users, signalling a scramble between the search engine providers for access to one of the internet’s biggest untapped audiences.

Ebay is understood to have held talks with all three companies about ways to co-operate more closely, including carrying targeted messages supplied by one of the companies’ online advertising networks. The online auction company refused to comment on the talks.