Oil futures settled on Monday at their lowest levels since March, with U.S. prices under $48 a barrel, pressured by a weekly climb in U.S. oil-drilling rigs as a steep plunge in the Shanghai stock market fed worries about a slowdown in Chinese energy demand.

West Texas Intermediate crude fell by 75 cents, or 1.6%, to settlement $47.39 a barrel on the New York Mercantile Exchange. Brent crude the global oil benchmark, fell $1.15, or 2.1%, to $53.47 a barrel on London’s ICE Futures exchange. Both marked their lowest settlements since roughly mid-March. The Shanghai Composite Index slid 8.5% Monday, its worst daily percentage-point fall since February 2007, as worries mount that authorities are pulling back on measures to prop up the market.

The index’s plunge lead to “fears of reduced demand” from China, said Joseph George, commodity analyst at Schneider Electric. China is the world’s second-largest energy consumer. Oil prices were also pressured by data released Friday from Baker Hughes Inc.  which showed that the number of oil-drilling rigs in the U.S., a rough proxy for activity in the industry, increased by 21 in the latest week, the largest gain since February 2014. “U.S. producers continue to drill at the fastest rate in three decades despite lower prices,” said George. “U.S. production has yet to show signs of a substantial fall and oil markets remain oversupplied.”

WTI prices trade at less than half their level from a year ago. Prices entered a bear market last week after falling more than 20% since their peak in June. Prices are facing more headwinds in the second half of the year, analysts say. According to Adam Longson at Morgan Stanley, crude demand, which had supported prices earlier in the year, is near a seasonal peak and will decline into the fall. Meanwhile, production continues to be strong with supply returning from new Canadian projects coming online, he said. “U.S. producers could be coming to the point where they start considering growth…albeit still in a materially oversupplied oil market, as productivity in the major plays continues to impress,” said analysts at Deutsche Bank.