Burger King Holdings Inc. is selling itself to private equity firm 3G Capital in a deal valued at $3.26 billion.

Thursday's $24-per-share offer comes after a day of speculation about the deal sent shares up more than 15 percent. The stock continued to make big gains Thursday before the stock market opened.

Burger King is the nation's second-largest hamburger chain behind its far-larger rival McDonald's Corp. But with 12,100 locations, it's struggled because the economy has been bad for its most important group of customers: young men.

Under the terms of the deal with 3G, Burger King's Chairman and CEO John Chidsey will become co-chairman of the board. 3G Managing Partner Alex Behring will be the other co-chairman.

Burger King became publicly traded in 2006, four years after a consortium of private equity firms acquired the company.

The group — TPG Capital, Bain Capital Partners and Goldman Sachs Funds — still own 31 percent of Burger King's outstanding shares and have agreed to tender their stock in the deal.