Experimental and theoretical studies have been carried out to elucidate the mechanism of water sensitivity of Berea sandstone and to quantify a number of important parameters. Based on the results of a number of novel experiments, a physical model has been developed. In this model, clay particles are released only when the salt concentration falls below a critical salt concentration. These colloidal clay particles remain dispersed in fresh water and are carried with the flowing fluid until they are captured at a local pore constriction, thereby decreasing the permeability. A mathematical model based on this mechanism has been developed. This model contains two parameters stemming from the rate equations of the release and capture of clay particles. Correlations of these parameters with flow rate and temperature are presented.