The illegal factory collected engine oil waste from vehicle maintenance plants and refined them by distillation. It then sold the refined oil to some gas stations, which in turn mixed the refined oil with diesel and sold them to motorists

The illegal business was said to be quite profitable as the city saw a fuel shortage and high fuel prices recently.

The factory owner would earn a profit of 400 yuan (US$49) per ton of refined oil, the quality supervision department said. It seized 20 tons of the refined oil and two tons of engine oil waste at the factory.

The oil was capable of damaging engines, the department said.

Legal oil refining required at least 17 different processes, while the illegal factory only took the simple step of distillation, it said. The factory would also pollute the environment near the site.