The present disclosure provides a method for detecting degradation of an engine oil, by separation into a polar component and a non-polar component via admixture with a polar solvent having a polarity index greater than or equal to 5 and optionally a non-polar solvent having a polarity index of less than or equal to about 1. The polar component is analyzed for one or more degradation indicators selected from the group consisting of antioxidants, acid content, and combinations thereof. Such degradation indicators relate to a degree of engine oil degradation. The polar component may be analyzed by Gas Chromatography and Mass Spectrometry (GC/MS) for the one or more degradation indicators, which can provide a semi-quantitative level of such degradation indicator species. The non-polar component identifies combustion products that help to explain the level of degradation.