The oil resistance of rubber refers to the ability of vulcanized rubber to resist the action of oils. When rubber products are in long-term contact with various oils, the oils can penetrate into the rubber, causing it to expand or increase in volume. On the other hand, oil-based media can extract soluble compounding agents (such as plasticizers, etc.) from the vulcanized rubber, causing the vulcanized rubber to shrink or lose volume. This is a dynamic equilibrium process; If the volume change caused by swelling is greater than that caused by contraction, it shows expansion. Conversely, it will contract. The oil resistance of rubber usually refers to its resistance to non-polar oils, such as fuel oil, mineral oil and synthetic lubricating oil. According to the principle of like dissolves like: polar polymers dissolve in polar solvents, while non-polar polymers dissolve in non-polar solvents. Therefore, polar rubber has good stability against non-polar oils and is called oil-resistant rubber, such as nitrile rubber, fluorine rubber, fluorosilicone rubber, chloroprene rubber and acrylate rubber, etc. Non-polar rubbers, such as natural rubber, butyl rubber, ethylene propylene rubber, and butadiene rubber, are called oil-resistant rubbers.

Nitrile rubber has moderate oil resistance and good anti-swelling ability against both mineral oil and synthetic hydrocarbon lubricating oil. It is the most commonly used oil-resistant rubber. According to the SAEJ-200 classification system, the heat resistance oil grade of nitrile rubber is lower than that of fluorine rubber and fluorosilicone rubber. However, the price of nitrile rubber is much lower than that of fluorine rubber and fluorosilicone rubber, and it has good processing performance. Therefore, it has become one of the widely used rubber types and is the rubber with the largest consumption in rubber sealing products. The polarity of nitrile rubber increases with the increase of acrylonitrile content, and its oil resistance improves, but its low-temperature resistance deteriorates. Therefore, in use, it cannot solely rely on increasing the acrylonitrile content in the raw rubber to enhance its oil resistance.