A modified conduction model is proposed for predicting the maximum local electric field, current density and attractive force between two spherical particles in a host oil. The dependence of the conductivity of the host fluid on electric field is expressed by a simplified equation based on Onsager's theory. The model gives the ratio of the maximum local field to the applied field as Em/E0=30(Г/A)0.1 (Ec/E0)0.9, where Г=бp/бf (0) and бf (0), A and Ec are the conductivity parameters relating to the host fluid. бp is the conductivity of the particles and E0 the applied field. Good agreement is found between the predicted and measured values of the current density and the yield stress of electrorheological (ER) suspensions. To obtain a strong ER effect, a high value of the combined conductivity parameter of the host fluid λ=Kf [бf(0)A]-0.1 (Ec)0.9 is desired.