While the dielectric properties of oil itself are well known, neither the dielectric constant nor the resistivity of a multiphase system consisting of a matrix with clay, containing oil and more or less water, is at all well known. Presented herein are some measured values of the dielectric constant based on a preliminary study of multiphase systems consisting of (1) an unconsolidated clay-sand mixture with varying percentages of oil over the frequency range 20 MHz to 1 GHz, and (2) a sandstone core with clay inclusions containing oil, over the same frequencies. The behavior of dielectric constant shown is significant in the interpretation of microwave logging and electromagnetic geotomography data and further improvement of these techniques.