The single-well chemical tracer test has been used previously toumeasure residual oil saturation in oil reservoirs. In this thesis it hasbeen extended to include the effects caused by mobile oil and the leach-ing of mutually soluble components from the oil phase by the injectedbrine.The theory of two-phase flow is combined with the theory of tracermovement in two-phase multicomponent systems. Numerical solutions oftracer tests in an idealized reservoir are used to study the effects ofmobile oil and leaching by detailed simulation. A tracer in mobile oil does follow its theoretical characteristicsaturation, if such a saturation is available. The simulations describedin this thesis are used to predict apparent residual oil saturations thatcompare well with the theoretical characteristic values.When mutually soluble components are present in the oil, their effecton the tracer test results is dependent on the relative frontal veloci-ties of the tracers and the soluble components. If the tracers move intothe formation ahead of the dissolution front, they are relatively unaf-fected by the leaching process. If the tracers are behind the dissolu-tion front, they encounter lower oil saturations. The apparent SOR meas-ured is thus affected by the leaching process.