Radio frequency electromagnetic fields are used to excite earth formations in the vicinity of a well borehole. The total field amplitude at a single coil receiver and at a dual coil receiver are detected and signals representative thereof are combined according to a predetermined relationship to obtain the relative permittivity and resistivity of the earth formations. By combining the measured permittivity with porosity measurements from another source according to predetermined relationships, the water saturation S.sub.w and residual oil saturation ROS may be determined and logged as a function of borehole depth.