China overtook the US as the world’s biggest importer of crude oil in April, the culmination of a seismic shift in global energy flows over the past decade.

Chinese customs data showed crude oil purchases from overseas hit a new high of 7.4m barrels a day in April, equivalent to roughly one in every 13 barrels consumed globally and topping US imports of 7.2m b/d. The US routinely exports about 500,000 b/d, The Financial Times reported.

While China’s imports are not expected to consistently surpass those of the US until the second half of this year, the move illustrates how the US shale revolution has cut the country’s reliance on oil from overseas — and how China’s demand has grown even as its economy slows.

Colin Fenton, managing partner at Blacklight Research, said China’s imports increased as it stockpiled oil. “It’s begun,” Fenton said. “China’s crude imports have been above trend in four of the past five months.”

The jump in imports last month was partly down to higher shipments from Iran, according to consultancy Energy Aspects. China Oil also bought a record number of Oman and Abu Dhabi crude cargoes last month, in a public trading window that helps determine the region’s benchmark prices.

“Iran may be offering more discounts on its oil as part of an effort to increase ties with Chinese oil companies,” said Amrita Sen at Energy Aspects. “Iran is keen to secure more Chinese investment.”

China’s state-backed traders, including Unipec and China Oil, are taking a much more visible role in the global crude market. They have steadily built up more sophisticated operations to compete directly with established trading desks at western oil companies like BP and Royal Dutch Shell, banks like Goldman Sachs, and commodity dealers like Vitol and Glencore.

In the US, higher prices and more efficient motor vehicles curbed consumption in the aftermath of the financial crisis, while the surge in shale oil output over the past three years has reduced imports.

Producers are now chafing at government restrictions on US crude exports that date back to the oil shocks of the 1970s. “It makes no sense that other countries can sell their crude into US markets, while US crude is essentially landlocked,” said Doug Suttles, chief executive of the Encana oil and gas company.

US imports could rebound in the short term, traders say, with fuel demand boosted by the collapse of oil prices to $65 a barrel. The price fall has also sharply reduced drilling activity in US shale regions such as North Dakota.