MELBOURNE, Jan 11 (Reuters) - Oil prices rose on Tuesday after two days of losses, with some risk appetite returning as the market awaited clues from the U.S. Federal Reserve chairman on potential rate rises and as some oil producers continued to struggle to beef up output. Brent crude futures gained 26 cents, or 0.3%, to $81.13 a barrel at 0156 GMT, after dropping 1% in the previous session. U.S. West Texas Intermediate (WTI) crude futures rose 30 cents, or 0.4%, to $78.53 a barrel, after falling 0.8% on Monday.