A method for determining the electrical properties of a core sample having an initial saturation Sw0, an initial true resistivity Rt0, and a porosity ϕ, including the steps: preparing a brine having a resistivity Rw, flushing the core sample with the brine, determining a first true resistivity Rt1 at a first saturation Sw1, once the resistivity Rw of the brine going into the core sample is the same as the resistivity Rw of the brine going out of the core sample, determining a function Rt=f(Sw) describing the dependency of the true resistivity Rt of the core sample and the saturation Sw in the core sample, based on the initial saturation Sw0, initial true resistivity Rt0, first true resistivity Rt1, and first saturation Sw1, second true resistivity Rt2, and first saturation Sw2, determining the resistivity Ro of the fully saturated core sample by estimating the function Rt=f(Sw) to full saturation of the core sample at Sw=100%, determining a resistivity index





I
R

=


R
t


R
o






at the Sw, Sw1, Sw2 determining a saturation exponent n using linear regression of the log-log plot of IR vs. Sw.