We measured the dielectric permittivity of dry and fluid saturated Green River oil shale samples over a frequency range of 1 MHz to 1.8 GHz. Dry sample measurements were carried out between room temperature and 146 degrees C; saturated sample measurements were carried out at room temperature. Samples obtained from the Green River formation of Wyoming and from the Anvil Points Mine in Colorado were cored both parallel and perpendicular to layering. The samples, which all had organic richnesses in the range of 0.04-0.19 L/kg (10-45 gal/ton), showed small variations between samples and a relatively small level of anisotropy of dielectric properties when dry. The real and imaginary part of the relative dielectric permittivity of dry rock was nearly constant over the frequency range observed, with low values for the imaginary part (loss factor). Saturation with deionized water and brine greatly increased the values of the real and imaginary parts of the relative permittivity, especially at the lower frequencies. Temperature effects were relatively small, with initial increases in permittivity to about 60 degrees C, followed by slight decreases in permittivity that diminished as the temperature increased. Implications of these observations for the in situ electromagnetic or radio frequency heating of oil shale to produce oil and gas are discussed.