The in situ electrical conductivity and permittivity of Colorado oil shale were recently measured. The measurements were made by transmitting a high frequency electromagnetic signal from one borehole to adjacent boreholes arranged in line. The in situ electrical conductivity and permittivity were then calculated from transmission measurements from the transmitter borehole to two receiver boreholes spaced in a line away from the transmitter borehole. The differential signals between the two receiver boreholes were used in our calculations.