New York's main contract, light sweet crude for delivery in October, shed eight cents to $97.09 a barrel and Brent North Sea crude for October delivery fell six cents to $115.34.
"On the commodity front, oil did very little... although that could swiftly change after Thursday's Fed meeting," IG Markets said in a report.
Market speculation was high that the Fed's Federal Open Market Committee would announce new economic stimulus at the end of a two-day meeting Thursday.
But just how far the committee will go, and what kind of impact it can have, is unclear, analysts said.
Traders were also eyeing the US Department of Energy's weekly US petroleum supplies report due later Wednesday, to gauge demand in the world's biggest oil-consuming country.
In Europe, attention is on a German constitutional court ruling on the European Stability Mechanism, the eurozone financial aid fund, with expectations high that the court will approve its use.