European antitrust regulators have been in informal discussions with Microsoft Corp. (MSFT) about their Internet search collaboration with Yahoo Inc. (YHOO), Microsoft said Thursday, although it is not clear whether the European Commission will formally review the deal.

Microsoft and Yahoo in July agreed on a long-awaited pact to work together on Internet search advertising, a deal aimed at better combating the market leader, Google Inc. (GOOG).

Discussions with the Commission have been taking place for several weeks, a Microsoft spokesman said. Last week, the U.S. Department of Justice said it was requesting more information from the companies, indicating the possibility of a longer review.

"As we said when the agreement was announced, we anticipated that this deal will be closely reviewed in the United States and the E.U., and discussions in both geographies continue," Microsoft spokesman Jack Evans said.

He reiterated that Microsoft hopes the deal will close early in 2010.

The European Commission hasn't announced its intention to formally review the deal and it remains unclear whether it will do so.

Market leader Google's market share of the paid Internet search market in Europe, at roughly 92%, is higher than in the U.S., where it is just under 80%.

Microsoft's shares closed Thursday up 0.4% at $25.30.

-By Jessica Hodgson, Dow Jones Newswires; 415-439-6455; jessica.hodgson@dowjones.com