China’s independent refiners have driven a meteoric shift in the global oil market since Beijing gave them permission to import crude in 2015, helping the nation overtake the U.S. as the world’s biggest importer and shaking up trade flows. Private processors underpinned a market recovery in 2020 after the Chinese economy rebounded from the Covid-19 pandemic, buying so much cheap oil at one stage that a traffic jam of tankers formed off the coast as they waited to unload millions of barrels.