With the OSI one can study the effects of various levels and types of anti- or pro- oxidants. In the chart below an oil had various levels of a pro-oxidant (copper) added. With no anti-oxidants added to the oil the blue line shows the loss of stability with increasing pro-oxidant. A free radical absorbing anti-oxidant (A) was added in the black line.  With no pro-oxidant present it greatly increased the stability of the base oil, but even with a small amount of copper (100 ppb) added the stability drops by a factor of two.  Another anti-oxidant (B) that chealates metals is added in the green line. It preserves the oil's stability, but does not increase it over the base oil. However, when both types of anti-oxidant are present the oil's stability is increased synergistically and maintained even in the presence of high levels of pro-oxidant.

 
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