Oil Oxidation

Written by: Allan Zieser, STLE, CLS

All oils oxidize in the presence of the most abundant gas on the planet, oxygen. Oxygen is all around us and for the most part, it is a good thing. However, in hydrocarbon lubricants oxygen can bond with elements in your lubricants which cause the oil to thicken and form sludge and varnish. This can occur either while a lubricant is in use or in storage.

While oxygen is the major factor in oil oxidation there are other factors that contribute to the oxidation of your lubricants.

Heat is a major contributor to oxidation as the oxidation rate of lubricants increases in the presence of heat. The higher the temperatures the faster the rate of oxidation.

Ultraviolet light is another contributor to oil oxidation, lubricants should not be stored in clear containers because of this.

One more factor that speeds oxidation, but not directly, is water. Water does contain oxygen, but it takes a lot of energy to break the water down so that the oxygen can damage the oil. The main reason that water effects oxidation is that water breaks down the additives that are formulated into the oil to prevent oxidation. With these additives damaged or missing the oil will oxidize at an increased rate.


While there is no way to prevent oxidation, you can slow its progress with your lubricants. Here are some steps that you can take to slow oxidation.

  • Keep oil containers sealed or closed until you need the product. Reseal the containers after using them.
  • Store your lubricants in a cool, dry environment.
  • Avoid the use of clear containers.
  • Air control is one of the easier ways in circulation systems to slow oxidation. Make sure that your systems have tight seals and joints to prevent air from entering the system or becoming entrained into the oil.


With a little thought to the storage and use of your lubricants, you can increase the life of the lubricants and your equipment which saves you time and money.