NEW YORK, Dec. 20 (Xinhua) -- Oil prices kept rising Wednesday as official data showed a larger-than-expected drop in U.S. crude stockpiles. The West Texas Intermediate for February delivery increased 0.53 U.S. dollar to settle at 58.09 dollars a barrel on the New York Mercantile Exchange, while Brent crude for February delivery added 0.76 dollar to close at 64.56 dollars a barrel on the London ICE Futures Exchange.