Laboratory measurements on the radio-frequency (10–103 MHz) electrical behavior of Green River oil shales were carried out using an automated frequency domain technique. Data are presented which show the variation of the relative dielectric constant (ε′), dielectric loss (ε″), and loss tangent (tan δ) with shale oil yield, frequency, temperature, and water content. The magnitude of these electrical parameters is shown to be sensitive to water content and possibly to varve geometry. The ε′ values tend to decrease and tan δ increases with increasing oil yield for shales subjected to prior thermal treatment at ~110 °C for 1–2 weeks. A systematic variation is observed in the degree of scatter and in the extent of correlation of tan δ and ε′ as a function of oil yield with each subsequent thermal treatment cycle. The manner in which variations in shale water content and (or) varve geometry influence the magnitude of the measured dielectric parameters is illustrated by duplicate measurements on samples with identical organic content. Such effects are shown to be important at low measurement frequencies (< 200 MHz). The temperature dependence of ε′ and ε″ is seen to be weak in the range 25–250 °C and appears to be largely dominated by temperature-induced changes in the water content of the shale.