Regulations governing diesel engine emissions into the atmosphere have led to changes in engine design resulting in increased soot loading of the oil. The largest contaminant in diesel engine lubricating oil on a mass percentage basis is soot. A new instrument named LEM, designed to measure the concentration of soot in diesel engine lubricating oil and the existing methods of measuring soot are described. Comparisons of measurements of the amount of soot in diesel engine oil by the test methods have been conducted. The test results are compared to the expected theoretical results to allow a comparison of the accuracy of the test methods.