Resistance to breaking down in the presence of oxygen is a key factor in extending the useable life of a product. A lubricant’s resistance to oxidation is decided by the very base oil chosen as well as the components of the additive package. It is worth mentioning that, while some additives classified as antioxidants and corrosion inhibitors can protect the lubricant and equipment respectively, there are some additives that may reduce oxidation resistance. This is an example of why formulation balancing is key to success, while overtreating a product with excessive additives can be counter-productive.
The two tests reported most frequently on data sheets for oxidation resistance are established American Society for Testing and Materials (ASTM) methods. The following information was intentionally written without going into the minutia of the methods and is intended only as an introduction to the concepts.