Price of lubricating oil on markets has still not decreased while crude oil has decreased by 70% compared to top level of 140 USD/container. For example, at Chau's store in D3 Street, Binh Thanh district, price of lubricating oil of some foreign trademarks has changed from 55.000 to 66.000 VND/tank/litre, the average price of domestically-produced lubricating oil was from 35.000 to 48.000 VND/tank/litre. The given reason was that lubricant was not produced from original oil (a product of crude oil) while original oil is not directly related to crude oil. It meant that decrease in crude oil did not make original oil decreased in price. However, many people think that it is not reasonable for lubricant to reduce in price when the price of crude oil decreased. To minimize loss for consumers, it is necessary for functional agents to intervene, supervise the price of imported original oil and ask companies for announcing mixing formula, then calculate the product price.