It displaced Saudi Arabia as China’s biggest provider after a 55% increase over the past year allowed the Chinese state to capitalise on low prices brought about by western countries refusing to buy oil from Russia.
Russian oil exports to China totalled nearly 8.42million tonnes in the month of May, nudging out Saudi Arabia which exported 7.82million tonnes to China.
Chinese state giants Sinopec and Zhenhua Oil have increased their purchases of Russian crude in recent months, refining the oil and selling it on.
Discounts of up to 30% have undermined western sanctions and sparked fears that Russia will continue to find funding for its war in Ukraine.
Last week, the Centre for Research on Energy and Clean Air think tank said Russia earned almost $100bn in revenue from fossil fuel exports in the first 100 days of the country’s invasion of Ukraine.
The European Union made up 61% of these imports, worth approximately $59bn.
Oil prices have risen by more than 60% over the past 12 months, topping $112 a barrel for international benchmark crude as of Monday.