Microsoft is understood to have made a $44.6bn (£22.4bn) bid for Yahoo!. The offer values the internet service provider at 62% more than its share price when the market closed yesterday.
The technology giant is known to be interested in acquiring Yahoo! and speculation has been mounting since last year. The talks come at a crucial time for both Microsoft and Yahoo!, which are both fighting for a share of the digital advertising space, against Google, the market leader.
Microsoft acquired a 1.6% stake in social networking site Facebook for $240m (£121m) last year. It beat Google to buy the stake, which values Facebook at $15bn (£7.5bn). The deal gives Microsoft exclusive global rights to place third party banner ads on the site.
Google already handles the search-related ads on rival social network MySpace and serves as its main search engine.
The Yahoo! bid comes in the same week that Microsoft announced it would handle the search and contextual links for the Wall Street Journal. It announced the deal earlier this week.