During the test, the lubricating grease is exposed to pure oxygen inside a hermetically sealed pressure chamber at an elevated temperature. The oxygen is consumed by the process of oxidation, which in turn lowers the pressure in the pressure chamber. Given that there are oxidation inhibitors in the lubricating grease, this drop in pressure can be prevented for as long as the additives can buffer the oxygen.
Ageing is simulated for a specified time (typically 100 or 200 h). The result is a drop in pressure during this period. The oxidative stability of the lubricating grease as a whole is determined, not just that of the separated base oil. The values that are ascertained from this process indicate the oxidative stability of the grease in its practical application. The longer it takes for the drop in pressure to register, the better equipped the grease is against premature ageing.