It is forbidden to transport gasoline in plastic barrels, and a conductive rubber is often dragged behind the tanker. this is because

Plastic and oil belong to different substances. When they rub against each other, one object is positively charged and the other is negatively charged. Because plastic is an insulator, it can't conduct charge to the earth in time. When they discharge, they will produce electric sparks, which will easily ignite the gasoline in the plastic bucket. Therefore, it is forbidden to transport gasoline in plastic barrels. There is often a conductive rubber sweeping the floor behind the car transporting fuel, because the earth and conductive rubber are conductors, and the conductive rubber will conduct the charge on the fuel tank to the earth to avoid accidents.

So the answer is: the mutual friction between oil and container wall makes the container charged, which is easy to cause electric spark.