Some analysts believe the central bank will launch a third round of bond-buying due to recent weak economic data from the United States such as disappointing jobs numbers on Friday.
Additional stimulus would likely weaken the dollar, boosting the price of dollar-denominated commodities like oil.
Lingering geopolitical worries also helped put a floor under prices on Tuesday.
Israeli Prime Minister Benjamin Netanyahu said his country and the United States were in talks on setting a "clear red line" for Iran's nuclear programme, but the two allies remained at odds over whether to spell out a clear threshold for military action against Tehran.
Brent crude was trading 23 cents higher at $115.04 a barrel by 0847 GMT, after settling up 56 cents on Monday. US crude was up 2 cents at $96.56.
"Prices have barely moved, suggesting the market is in waiting mode (ahead of the Fed gathering)," said Tetsu Emori, a Tokyo-based commodities fund manager at Astmax Investment.
"(Fed Chairman Ben) Bernanke has clearly said that the employment situation (in the US) is not good, so there's a chance (of quantitative easing)."