Surface conductivity is indicated by electrical resistivity dispersion in low water saturation. When evaluating surface conductivity, the pore geometry should be considered because a large structure is easier to saturate rather than a small structure. This work underlines the evaluation of pore geometry distribution and saturation degree of reservoir rock and its effect to electrical dispersion. It is found that pore radius distribution and porosity has a good correlation with electrical dispersion. The large structure reflects more electrical dispersion compare to the small one. In high water salinity, surface conductivity occurs at low water saturation degree and vanishes with more water saturation addition. The potential indicator to estimate rock porosity derived from electrical dispersion has been verified in this article. © 2013 Copyright Taylor and Francis Group, LLC.