Oil prices fell in Asian trading on Thursday after a larger-than-expected Federal Reserve interest rate cut sparked concerns about the U.S. economy.

Oil futures trimmed losses Wednesday, after government data showed U.S. crude inventories fell last week and the Fed delivered a half-point rate cut.

The Brent/WTI spread has historically ranged between $4/bbl and $8/bbl, but it can expand or contract based on factors related to U.S. and international supply and demand conditions. For example, the Brent/WTI spread hit nearly $14/bbl in April 2011 when protests sparked market fears of significant oil supply disruptions in the Middle East.