The relentless flow of China’s excess fuel into the global market is showing few signs of easing, raising fears the torrent will eat into profits at rivals across the region.

The world’s second-biggest oil consumer shipped record amounts of diesel and gasoline overseas last year as increasing production capacity means Chinese refiners are producing more than the country needs. The unprecedented volume of exports is threatening to swamp Asian markets from South Korea to India, where higher crude prices are already eating into refining margins.

“Asian refining margins will inevitably be under pressure from this surge of exports from China,” said Li Li, a research director with ICIS China in Guangzhou. “Refiners across the region, including in Japan, South Korea and Malaysia, will all be negatively affected.”

If last year was bad for China’s neighbors, 2018 could be even worse. The country’s biggest energy producer warned last week that net oil-product exports may turn into a deluge as the government works to ease a supply glut in the domestic market. While surging demand for diesel has driven a rally in oil prices, the expected jump in exports from China may dilute the gains that can be made from selling the fuel in Asia.

The effect that China’s fuel exports can have on margins was illustrated in 2015 when cargoes from the nation swamped the Asian market, dragging profits from producing diesel in the region to below $8 a barrel and the lowest level in at least five years. The so-called crack spread was at $15.51 a barrel as of 4:30 p.m. Singapore time on Tuesday.

Outbound diesel shipments from China jumped almost 12 percent in 2017 to average 351,335 barrels a day, according to Bloomberg calculations based on data posted Tuesday on the General Administration of Customs website. Gasoline exports climbed 8.5 percent to about 240,434 barrels a day.

The Chinese government may encourage more flows overseas, an analyst at China National Petroleum Corp. said last week. The Ministry of Commerce awarded the first batch of fuel export quotas totaling 16.24 million tons under the general trade system to Chinese state refiners for 2018, according to officials at firms that received notices and who asked not to be identified because of internal policy.

“China’s fuel supply swelled last year with new refining units and higher output from independent refiners,” Li said. “With the quite generous export quotas for this year, outbound shipments will likely jump further.”