Resistivities of various suspensions, prepared by adding incremental amounts of rock powder materials (< 62 mu m) in NaCl brines of different salinities ranging from 10 to 200 kppm, were measured and compared. Results indicated a linearly increasing suspension resistivity with increasing volume of solid particles, on a semilogarithmic scale. Except for Wyoming bentonite, the relationships between the resistivity and volume of particles were similar for all materials measured at different brine salinities. An Archie-type linear relationship was observed between the suspension resistivity factor, which is the ratio of the suspension resistivity to the brine resistivity, and the fractional brine volume of the suspension. The slopes m of the linear relationships on log-log plots were comparable for all samples. The average slope was 1.708. The Wyoming bentonite exhibited different characteristics. Elimination of surface conductivity by using high salinity brines and increase of tortuosity due to the association of clay particles probably account for the higher slope (m = 2.852) for Wyoming bentonite.