Warren Buffett's Berkshire Hathaway Inc. (NYSE: BRK.A, BRK.B) said it has agreed to acquire chemical company Lubrizol Corp. (NYSE: LZ) for $135 a share in cash, or $9 billion, making it one of the largest acquisitions in its history.

The purchase price represents a 28 percent premium over Lubrizol’s closing price of $105.44 on Friday. The price excludes $700 million of debt.

Lubrizol is exactly the sort of company with which we love to partner - the global leader in several market applications run by a talented CEO, James Hambrick, said Buffett.

The companies expect the deal to close during the third quarter.

Wickliffe, Ohio-based Lubrizol, with 2010 revenue of $5.4 billion, comprises two business segments, Lubrizol Additives and and Lubrizol Advanced Materials. Founded in 1928, Lubrizol employs about 6,900 people.

Lubrizol's Additives segment covers engine oil, driveline and industrial additives, while Lubrizol Advanced Materials specializes in producing advanced specialty polymers, polymer-based additives and chemical additives.

Citi and Evercore Partners are acting as financial advisors to Lubrizol.