A six‐electrode cell measures both a horizontal and vertical resistivity on a single deformable sample under compacting load. The similar effects of anisotropy and sample thickness on the ratio of two voltages in the cell allow a determination of the anisotropy coefficient. The geometric mean resistivity is obtained using a cell constant appropriate to the electrically determined product of the anisotropy coefficient and sample thickness. Clay and shale materials have ratios of vertical to horizontal resistivity of from near unity to 25 to 1.