Noble gases widely exist in nature, and except for radon, they are stable. Modem techniques can detect noble gases to relatively low concentrations and with great precision. These factors suggest that noble gases can be useful tracers for subsurface characterization. Their applications, however, require an appropriate transport model for data analyses. A new fluid property module, EOSN, was developed for TOUGH2 to simulate transport of noble gases in the subsurface. Currently any of five different noble gases (except radon) as well as CO2 can be selected, two at a time. For the two selected gas components, the Crovetto et a]. [J. Chem. Phys. 76 (1982) 1077-1086] model is used to calculate the Henry's law coefficients; and the Reid et al. [The Properties of Gases and Liquids, McGraw-Hill, New York (1987)] correlation is used to calculate the gas phase diffusivities. Like most other sister modules, TOUGH2/EOSN can simulate non-isothermal multiphase flow and fully coupled transport in fractured porous media. Potential applications of the new module include, but are not limited to: (a) study of different reservoir processes such as recharge, boiling, condensation, and fracture-matrix fluid exchange; (b) characterization of reservoir geometry such as fracture spacing; and (c) analysis Of CO2 sequestration. (C) 2004 CNR. Published by Elsevier Ltd. All rights reserved.