The variability of rheological properties in fluid-mud suspensions is studied as a function of salinity and sediment concentration. It was found that the steady state shear stress increases exponentially with increasing sediment concentration and increases logarithmically by increasing the salinity of the suspension. An analytic model predicting shear stress as a function of electroviscous properties is developed. The model shows that the effect of salts in the suspension is to decrease the zeta potential by compressing the electric double layer and, thereby, elevating the shear stresses acting on the shearing planes at each particle-fluid interface in the suspension. These stresses increase with the increase in salt content. The model incorporates the classical double-layer theories of Gouy-Chapman and the Helmholtz-Smoluchowski theory for electrokinetics of charged particles. The model shows good correlation with experimental data at low sediment concentrations where the basic assumptions of the Gouy-Chapman formulation are satisfied. At progressively higher sediment concentrations, there are increasingly larger departures between the model predictions and the experimental data due to violations of these basic assumptions. The advantages and limitations of the model are discussed. ¿ American Geophysical Union 1994