Microsoft Corp. chief Steve Ballmer signaled his openness to a deal with Yahoo Inc., sending Yahoo shares up as much as 15% on investor hopes that Microsoft's failed bid for the Internet company might rematerialize.

After the comments touched off a surge in Yahoo shares, Microsoft tried to play down its chief executive's comments. "Our position hasn't changed," a Microsoft spokesman said. "Microsoft has no interest in acquiring Yahoo. There are no discussions between the companies."

Mr. Ballmer, speaking Thursday at a technology conference in Orlando, said a deal with Yahoo "would make sense economically." Mr. Ballmer was referring to a hypothetical agreement to acquire Yahoo's search business, though some interpreted his comments to be about a full-blown acquisition of Yahoo.

Mr. Ballmer also cautioned in his speech that Microsoft wasn't in any discussions with Yahoo about a deal and that Yahoo wished to remain independent.

A Yahoo spokesman declined to comment. The company's shares closed up 11%, or $1.24, at $12.99 on the Nasdaq Stock Market.

Mr. Ballmer's comments, and the investor reaction to them, underscore how the issues prompted by Microsoft's original effort to acquire Yahoo remain unresolved. Earlier this year, Microsoft abandoned an unsolicited bid of $33-a-share to acquire Yahoo, worth nearly $50 billion.

Microsoft remains determined to bolster its online-advertising business, a market in which Google Inc. continues to grab most of the profits. And Microsoft hasn't completely ruled out the possibility of a Yahoo deal in the future.

Investor Carl Icahn, who joined the Yahoo board after a settling a proxy battle with the company this summer, continues to agitate for Yahoo and Microsoft to combine. Appearing on CNBC earlier this week, Mr. Icahn said Yahoo and Microsoft still need each other -- a sentiment he has expressed publicly before and in conversations with other Yahoo board members.

Whether Mr. Icahn can convince his fellow board members to try to rekindle a deal remains unclear. He couldn't be reached for comment Thursday,

Meanwhile, Yahoo continues to consider a merger with Time Warner Inc.'s AOL, a deal both sides have been discussing for months. While talks continue in earnest, price has remained a major barrier, especially in the deepening economic crisis.

One person familiar with the situation said a deal between Microsoft and Yahoo may not preclude a Yahoo-AOL combination. An idea that had been floated and previously reported was to have Microsoft buy Yahoo's search business and then merge the remainder of Yahoo with AOL. However, that scenario has not been discussed in any serious way, this person added.

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Merissa Marr contributed to this article.