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A new vacuum-oven sublimation method (PVOS) for measuring the hydrocarbon fraction of diesel particulates has been developed to overcome problems with the standard vacuum-oven sublimation technique (VOS). VOS gave extremely low (negative at 15:1 A/F) results for diesel particulate samples taken at medium to high load (25:1 or lower A/F). The low results are due to the adsorption by the samples of trace amounts of continuously regenerated (from test samples and oven seals) heavy-hydrocarbon oven contaminants. PVOS corrects the problem by using a nitrogen gas purge to sweep hydrocarbons from the oven during testing. Comparisons among PVOS, VOS and methylene chloride extraction (MCE) over a range of A/F and engine speeds showed that PVOS results correlate more closely with MCE results than do results determined by the standard VOS technique.