Oil extended losses below $48 a barrel Tuesday amid speculation that U.S. inventories will expand, deepening a global supply glut that's driven prices to a five-year low.

Futures declined for a fourth day. Stockpiles in the world's biggest oil-consuming country probably rose by 700,000 barrels last week, a Bloomberg News survey showed before a government report Wednesday.

Oil slumped almost 50 percent in 2014, the most since the 2008 financial crisis, after the Organization of Petroleum Exporting Countries resisted calls to cut output as it competes with U.S. producers. The market faces "more problems" this year, according to Morgan Stanley, with surging output in Russia and Iraq contributing to a surplus that Qatar estimates at 2 million barrels a day.

"The path of least resistance is lower," said Bill O'Grady, chief market strategist at Confluence Investment Management in St. Louis, which oversees $2.4 billion. "There is no bullish news. OPEC refuses to cut production and there is no evidence of falling production outside of OPEC."

West Texas Intermediate crude oil for February delivery dropped $2.11, or 4.2 percent, to $47.93 a barrel on the New York Mercantile Exchange, the lowest settlement since April 2009. The volume of all futures traded was about 55 percent above the 100-day average for the time of day.

Prices were little changed after the American Petroleum Institute was said to report a decrease in U.S. inventories. Stockpiles declined 4 million barrels last week, the API said, according to a Twitter posting by Dominick Chirichella. West Texas Intermediate was down 4.1 percent in electronic trading Tuesday evening.

Brent for February settlement decreased $2.01, or 3.8 percent, to $51.10 on the London-based ICE Futures Europe exchange, also the lowest since April 2009.

"The market is obsessed with the supply side," Hans van Cleef, energy economist at ABN Amro Bank NV in Amsterdam, said by phone. "Prices have dropped too fast and too far, but with the market this negative it's hard to see a trigger which could turn the sentiment."

U.S. crude inventories probably increased to 386.2 million barrels in the week ended Jan. 2, according to the Bloomberg survey before the Energy Information Administration releases its weekly report Wednesday.

"Supplies may continue to rise here in the U.S. The supply glut is just weighing on everything," said Phil Flynn, senior market analyst at the Price Futures Group in Chicago.