The effect of dissolved CO2 on the electrical conductivity and viscosity of three NaCl solutions covering the range of salinity usually encountered in potential CO2 storage geological formations has been studied. At a constant temperature of 35 degrees C, the variations of conductivity and viscosity are proportional to the mole fraction of dissolved CO2. For viscosity, our data are in agreement with previous observations. The observed variations are small and are at maximum on the order of 10 %. The variations of conductivity and viscosity as a function of temperature up to 100 degrees C are not modified by the presence of CO2, and we suggest using the empirical Arps model. A simple model is proposed to take into account the small modifications of conductivity and viscosity as a function of the dissolved CO2 mole fraction and temperature.