Red oil is a historical heritage. Before the return of Hong Kong, there was no difference between red and white diesel oil under British law. However, industrial diesel is tax-free under British law, while automobile diesel is heavily taxed.

In order to distinguish the penetration of diesel oil and red dye used by the government in factories or industries, this law is implemented in all parts of Britain. When the customs spot checks find that vehicles use marked oil, users will be charged with tax evasion and fined several thousand yuan to confiscate the vehicles.

At present, the government has amended the legislation to exempt motor vehicle diesel oil tax. Diesel oil has been divided into industrial diesel oil and vehicle diesel oil in disguise, which is strictly enforced on vehicles. Sulfur-free diesel oil (high refining cost and high import price will not cause acid rain), marine/factory boiler oil and industrial marked oil (the government does not require sulfur-free diesel oil) are used in industry because of low refining requirements and relatively low import price. Illegal marked oil refers to diesel oil that has not been paid duty.