In the measurement of engine oil consumption the conventional radiometric method is more rapid and precise than the drain-weigh method, but the former method-a batch type-is inapplicable to measurements in transient engine operations which are inevitable in real driving. In the present study, a reliable method was developed to measure continuously the consumption rate through all phases of engine operation. Oleic acid sulfide containing S35 was selected as a radioactive tracer to be added to the engine oil. Engine exhaust gas containing the discharged oil was burned in an electric furnace and a gas burner and reacted with aqueous H2O2 solution, converting the S35O2 into H2S35O4. A plastic bead scintillator used for the detection of β-rays from the aqueous solution was sensitive enough to measure the consumption rate as low as 0.4 g/h. Some informative observations were also made on the oil consumption of the engine in transient and steady-state operations by use of this new measurement system.