NEW YORK, Dec 29 (Reuters) - The S&P 500 headed for its best December in nearly two decades as U.S. stocks advanced in thin trade on Wednesday, lifted by investor optimism about the economy in 2011.
The Dow Jones industrial average gained 9.84 points, or 0.09 percent, to 11,585.38, according to the latest available figures. The Standard & Poor's 500 Index gained 1.29 points, or 0.10 percent, to 1,259.80. The Nasdaq Composite Index gained 4.05 points, or 0.15 percent, to 2,666.93.
(Reporting by Edward Krudy; Editing by Kenneth Barry)