Abstract: A method is provided for precisely and concurrently measuring dynamic engine oil consumption and fuel consumption within an internal combustion engine on a real-time basis. Nonradioactive organo- bromine or chlorine compounds are added to the oil in small amounts in their natural isotopic abundance or enriched. Upon complete combustion, the bromine or chlorine is converted into hydrogen bromide (HBr) or hydrogen chloride (HCl), respectively. A tunable diode laser spectrometer is used to determine the trace amounts of the resultant HBr or HCl in the exhaust gases, which continuously flows through a sample cell by the use of a sample line that allows the unimpeded transport of samples, reduces the pressure of the exhaust gas and maintains it at a suitable level for analysis, and prevents the condensation of water vapor in the exhaust gas so as to prevent the dissolution of the tracer compounds in the water condensate.