In the 80's it was a common practice in the study of contamination by NAPL to incorporate a tracer to the medium to be studied. At that time the first applications focused on the use of 222Rn, a naturally occurring radioactive isotope as a natural tracer, appropriate for thermodynamics studies, geology and transport properties in thermal reservoirs. In 1993 the deficit of radon was used to spot and quantify the contamination by DNAPL under the surface. For the first time these studies showed that radon could be used as a partitioning tracer. A methodology that provides alternatives to quantify the oil volume stored in the porous space of oil reservoirs is under development at CDTN. The methodology here applied, widens up and adapts the knowledge acquired from the use of radon as a tracer to the studies aimed at assessing SOR. It is a postulation of this work that once the radon partition coefficient between oil and water is known, SOR will be determined considering the increased amount of radon in the water phase as compared to the amount initially existent as the reservoir is flooded with water. This paper will present a description of the apparatus used and some preliminary results of the experiments. © Owned by the authors, published by EDP Sciences, 2013.50 Cooke Jr., C.E., (1971) Method of Determining Residual Oil Saturation in Reservoirs, , U.S. Patent 3 590 923, Exxon Production Research Co. (July 6)Deans, H.A., Majoros, S., (1980) The Single Well Chemical Tracer Method for Measuring Residual Oil Saturation, , Final report, DOE/BC20006-18, (October)Tang, J.S., Harker, B.C., Interwell tracer test to determine residual oil saturation in a gas-saturated reservoirPart I: Theory and design (1991) JCPT, 30 (3), pp. 76-85. , May-JuneMinquan, J., Partitioning tracer test for detection, estimation and remediation performance assessment of subsurface nonaqueous phase liquids (1995) Water Resources Research, 31 (5), pp. 1201-1211Wilson, R.D., Markey, D.M., Direct detection of residual nonaqueous phase liquid in the saturated zone using SF6 as a partitioning tracer (1995) Environmental Science & Technology, 29, pp. 1255-1258Nicole, T.N., Brusseau, M.L., Field study of the partitioning tracer method for detection of dense nonaqueous phase liquid in a trichloroethenecontaminate aquifer (1996) Environmental Science & Technology, 30, pp. 2859-2863Semprini, L., (1986) Modeling and Field Studies of Radon-222 in Geothermal Reservoirs, , Ph.D. Dissertation, Stanford UniversityHopkins, O.S., (1994) Radon-222 As An Indicator for Nonaqueous Phase Liquids in the Saturated Zone: Developing A Detection Technology, , Master's Thesis, Oregon State UniversityGottipati, S., (1996) Radon-222 As A Tracer for Performance Assessment of NAPL Remediation Technologies in the Saturated Zone: An Experimental Investigation, , Master's Thesis, Oregon State UniversityHunkeler, D., Hoenh, E., Höhener, P., Zeyer, J., 222Rn as a partitioning tracer to detect diesel fuel contamination in aquifers: Laboratory study and field observations (1997) Environmental Science & Technology, 31, pp. 3180-3187Wentworth, C.K., A scale of grade and class terms for clastic sediments (1922) J of Geology, 30, pp. 377-392Clever, L.H., (1979) Solubility Data Series, Volume 2: Krypton, Xenon and Radon-gas SolubilityInternational Union of Pure and Applied Chemistry, , Pergamon PressOxford/UKCantaloub, M., Higginbotham, J., Semprini, L., (1997) The Determination of Rn Partition Coefficients for Several Liquid Scintillation Cocktails 43th Annual Conference on Bioassay, Analytical, and Environmental Radiochemistry, , Charleston, SC November 09-11Leal, J.M., (2008) Desenvolvimento da Tecnologia Do Pó de Turmalina, , Ph.D. Dissertation, Federal University of Ouro PretoLake, L.W., (1998) The Society of Petroleum Engineers Reservoir Characterization Course, , http://www.spe.org/web/training/demo/00frame.htm15/04/2010