DALLAS — Warren Buffett, the second-richest American, agreed to acquire Burlington Northern Santa Fe Corp. in a deal that values the Fort Worth-based railroad at $34 billion — Buffett's largest acquisition ever.

Buffett's holding company, Berkshire Hathaway Inc., already owns nearly 23 percent of BNSF, and it agreed to pay about $26 billion for the rest of the company, which operates the nation's No. 2 railroad. At $100 a share, the cash and stock offer represents a 31 percent premium over BNSF's closing price Monday.

Berkshire Hathaway would also assume $10 billion in debt from BNSF, the nation's No. 2 railroad.

Buffett described the transaction as a huge bet on the railroad business and on BNSF Chairman, President and Chief Executive Matthew Rose and his team.

“Most important of all, however, it's an all-in wager on the economic future of the United States,” said Buffett. “I love these bets.”

The boards of both companies have approved the transaction. The deal also requires approval by holders of two-thirds of BNSF's outstanding shares, other than the shares held by Berkshire Hathaway.

It's also subject to other closing conditions, including review by the U.S. Department of Justice. The deal is expected to close in the first three months of 2010, according to a statement by Berkshire Hathaway and BNSF.

“We are thrilled to have the opportunity to become a part of the Berkshire Hathaway family,” Rose said. “We admire Warren's leadership philosophy supporting long-term investment that will allow BNSF to focus on future needs of our railroad, our customers and the U.S. transportation infrastructure.”