A Hainan Airlines Boeing 737 carrying 156 passengers and eight crew took off in Shanghai and landed safely in Beijing on March 21, powered by a 50-50 blend of used cooking oil and normal jet fuel.

Boeing’s China president Ian Thomas described the flight as “a significant milestone” in China’s aviation industry. Biofuels can cut airlines’ carbon dioxide emissions by 80% compared to traditional jet fuels, but earlier plans to make these fuels from plant matter have proven tougher and more expensive than some predicted, forcing the US to cut quotas.
But China, which has already been ramping up wind power capacity and other clean energy sources, has an unusual advantage.

China has long struggled to contain its trade in “gutter oil,” a practice in which unlicensed vendors buy used cooking oil from some restaurants and resell it to others. At best, these vendors clean and process the oil before selling it on; at worst, they dredge old oil from drains that then they sell as new.

Last year, Boeing partnered with Commercial Aircraft of China to develop biofuel from precisely this kind of old oil, and the companies estimate China’s gutter oil supplies could produce 1.8 billion liters (476 million gallons) of biofuel every year.

In the future, the Chinese gutter-oil trade could collapse as restaurant owners, living on thin margins, shift to selling their old oil to airlines.