Oil futures extended losses in after-hours trading on Tuesday after a report showed U.S. crude stocks rose last week.
Crude inventories rose by 7.6 million barrels in the week to Aug. 28 to 456.9 million, compared with analysts' expectations for an increase of 32,000 barrels. Crude stocks at the Cushing, Oklahoma, delivery hub fell by 318,000 barrels, data from industry group the American Petroleum Institute showed on Tuesday.
U.S. crude futures were down 10 percent in extended trading, after closing down 7.7 percent, at $45.41 a barrel. On Monday it settled up $3.98, or 8.8 percent. Brent crude for October delivery were down $1, or 2 percent, to $49 a barrel.
Oil prices tumbled earlier after China's official Purchasing Managers' Index (PMI) dropped to 49.7 in August from 50.0 in July, reinforcing fears about slowing growth. Prices retreated after a three-day rally of more than 20 percent.
"It was primarily the China fear factor," Carsten Fritsch at Commerzbank in Frankfurt told the Reuters Global Oil Forum.
In another sign of faltering economic activity, data showed U.S. manufacturing sector growth slowed in August to its weakest pace in more than two years.