U.S. crude futures closed nearly 6 percent on Monday as weak economic data from China, the world's largest energy consumer, reversed a four-day rally from last week and an OPEC source undermined chances of an emergency meeting to stem the decline.
China's manufacturing sector contracted at the fastest pace since 2012 in January, adding to worries about demand from the world's second-biggest economy at a time when the market is already weighed down by a large supply overhang.
"China is the last standing consumer of oil outside of the U.S.. The problem is that everyone is relying on them," said Carl Larry, director of business development at Frost & Sullivan in Houston.
"As long as we keep in this scenario where China is the only real consumer to pick up the pace, we're going to see moves lower every time China has an issue with their economy."
Brent April crude futures were down $1.79, or 4.9 percent, at $34.20 a barrel, and had dipped as low as $33.92. The March Brent contract, which expired on Friday, settled at $34.74 a barrel.
U.S. West Texas Intermediate settled down $2, or 5.95 percent, at $31.62 a barrel. It hit a low of $31.29 earlier in the session.