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US oil settles down 4.1%, at $44.48 a barrel

Oil futures fell sharply on Wednesday after initially extending gains as government data showed a second consecutive weekly fall in U.S. crude oil inventories.

However, a build in gasoline inventories following the end of the U.S. summer driving season and falling refinery runs at the start of maintenance period offset the crude drawdown, John Kilduff, founding partner at Again Capital told CNBC.

U.S. light crude closed down $1.88, or 4.06 percent, at $44.48 a barrel. Benchmark Brent crude tumbled about 3 percent to $48.50 a barrel.

Gasoline demand was "the only thing keeping us alive there for the summer in terms of prices holding up," Kilduff said. "The downward press just keeps reemerging."

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The Energy Information Administration reported U.S. commercial crude stockpiles fell by 1.9 million barrels in the last week, compared with analysts' expectations for an decrease of 533,000.

Refinery crude runs fell 310,000 barrels per day, EIA data showed. Refinery utilization rates fell 2.2 percentage points to 90.0 percent of capacity.

Gasoline stocks rose 1.4 million barrels, compared with analysts' expectations in a Reuters poll for a 819,000-barrel gain.

Although total U.S. oil inventories are at record highs, the draw suggests a rebalancing of the biggest domestic oil market is under way as oil production slows in the face of low prices.

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The American Petroleum Institute (API) had earlier reported U.S. crude stockpiles fell 3.7 million barrels last week. That data had helped oil resist the negative impact of a sharp contraction in Chinese manufacturing.

Flagging demand is dragging China's factory sector into its sharpest contraction in 6½ years, a private survey showed on Wednesday, triggering a flight to safety in Asian markets that analysts say could extend across the globe.

The preliminary Caixin/Markit China Manufacturing Purchasing Managers' Index fell to 47.0 in September, its lowest since March 2009. Levels below 50 show a contraction.

Oil prices have been depressed for more than a year and are now trading at less than half their peak levels in 2014 thanks to massive oversupply by oil producers in the Middle East and North America.

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Many analysts say oil prices could be about to recover, but investors remain worried about China.

"China's economic slowdown continues, with factory output and investment growth both failing to hit targets," oil consultancy Energy Aspects said.

"With the economy showing little sign of recovery, the 7 percent GDP growth target set by the government may prove difficult to achieve," it added.

Energy Aspects said it expected global crude demand for the second half of the year to grow at only 1 million barrels per day (bpd), down from almost 2 million bpd in the first half.

—CNBC's Tom DiChristopher contributed to this story.