This method is designed to give a measure of the tendency of straight (i.e. plain) mineral lubricating oil to oxidize under specified conditions.

It employs the same apparatus and a similar procedure to those used to determine the oxidation stability of Inhibited Mineral Turbine Oil (BS 2000‑280). It differs from this test in that (a) the test time is reduced to 48 h, (b) two conditions, namely no catalyst and solid copper metal catalyst are used, and (c) the degree of deterioration is expressed as total oxidation products (TOP) per cent.