Microsoft has asked Yahoo to re-start talks on a possible merger or alliance, The NY Post is reporting. While Microsoft and Yahoo have held informal deal talks over the years, Post sources say the latest approach signals an added immediacy on Microsoft’s part that has up until now been lacking. The new approach follows an offer Microsoft made to acquire Yahoo a few months ago, but Yahoo rejected the company’s overtures. A deal between Microsoft and Yahoo would raise the combined companies’ share of the search advertising market to 27 percent against Google’s 65 percent, the article said. It would also narrow the gap in overall online ads with Google to just 13 percent. The Post cites Wall Street sources as putting a roughly $50 billion price tag on Yahoo. More to come.

Update: WSJ: In picking up from the Post’s coverage, the Journal wonders whether much has changed from a year ago, when negotiations between Yahoo and Microsoft fizzled. The Journal’s reasons for casting doubt on the merger:

-- Microsoft’s tendency to avoid large buys: Yahoo has 12,000 employees and earlier this week had a market value of $32 billion. Yahoo shares surged in overseas trading on news of the talks, raising the company’s market value to around $38 billion on Friday.

-- Yahoo execs’ distaste for Microsoft: Co-founder Jerry Yang, for one, has a reputation for disliking Microsoft and avoids using Microsoft products, a Journal source says. A merger could produce a mass exodus of top Yahoo staffers.

-- Instead of a complete merger, Microsoft could turn its online unit over to a separately run Yahoo, in return for a Yahoo stake, though a Journal source says Microsoft would be more likely to buy Yahoo outright. And it appears that some things that may have derailed the deal last year have changed, at least on the Microsoft side. Leaders of Microsoft’s online group who pressed for the company to rely on its own online search and ad systems have since left. But the biggest change since last year that might affect both Microsoft’s and Yahoo’s thinking: Google’s pending merger with DoubleClick.

• — Google Buys DoubleClick For $3.1 Billion In Cash