A radioactive tracer method was used to measure the contribution of engine oil to deposits on exhaust system components and particulates in the exhaust gas of a gasoline engine. The technique involves the use of an oil molecule labeled with radioactive 14C. By measuring the 14C concentration in engine deposits, the fraction of carbon derived from the lubricating oil can be determined. Results show that depending on the location of the deposit, oil contributes from 1 to 8% of the carbon deposited, and is independent of engine operating conditions. Oil contribution to particulate filtered from the exhaust gas ranges from 2 to 30% of the carbon, which increases in proportion to engine speed.