United Airlines (UAL) had the highest return in December 2009 by a large-cap US stock, returning 63.4%.

ASSET	MONTH	% RETURN
United Airlines (UAL)	December 2009	63.42%
New York Times (NYT)	December 2009	42.4%
NVIDIA (NVDA)	December 2009	42.27%
Micron Technology (MU)	December 2009	38.4%
Delta Air Lines (DAL)	December 2009	36.94%
Advanced Micro Devices (AMD)	December 2009	36.15%
Rambus (RMBS)	December 2009	34.66%
EXACT Sciences (EXAS)	December 2009	32.94%
Neurocrine Biosciences (NBIX)	December 2009	32.68%
Marvell Technology (MRVL)	December 2009	32.08%
Regeneron Pharmaceuticals (REGN)	December 2009	31.13%
Jabil Circuit (JBL)	December 2009	29.63%
Allegheny Technologies (ATI)	December 2009	29.56%
American Airlines (AAL)	December 2009	28.38%
Amkor Technology (AMKR)	December 2009	27.86%
Alcoa (AA)	December 2009	26.43%
Madrigal Pharmaceuticals (MDGL)	December 2009	25.87%
XPO Logistics (XPO)	December 2009	25.48%
Entegris (ENTG)	December 2009	24.24%
Cheniere Energy (LNG)	December 2009	24.11%
Gildan Activewear (GIL)	December 2009	24.07%
Southwest Airlines (LUV)	December 2009	23.5%
Centrais Elétricas Brasileiras SA - Eletrobrás (EBR.B)	December 2009	22.62%
T-Mobile US (TMUS)	December 2009	20.73%
Teradyne (TER)	December 2009	20.7%

Large-cap stocks are treated as having a market cap of $10B+.