The companies announced the agreement in July, in which Microsoft’s Bing search engine would power Yahoo’s search results, and Yahoo would provide premium search-advertising services for both companies.

They had hoped to finalize the deal in late October but needed more time to work out the details.

“Microsoft and Yahoo believe that this deal will create a sustainable and more compelling alternative in search that can provide consumers, advertisers and publishers real choice, better value, and more innovation," they said in a statement Friday. 

The deal is still facing an antitrust review by the U.S. Department of Justice. The companies said they "remain hopeful that the closing of the transaction can occur in early 2010.”