Improved laboratory measurements of mantle minerals under controlled thermodynamic conditions should be undertaken to extrapolate laboratory results to Earth conditions. In particular, the influence of minor elements such as hydrogen, nickel, and aluminum on the point defect populations that control solid-state conduction in olivines and pyroxenes should be determined. New experimental techniques are needed to study nonequilibrium electrical properties of water-saturated crustal rocks at elevated temperatures (50 to 500°C). Systematic experimental and theoretical studies of the electrical response of multiphase aggregates and networks should be undertaken to improve understanding of upper-crustal conductivities. Effects of the presence and distribution of other conductivity-enhancing phases such as carbon, magnetite, sulfides, and partial melts should be investigated using advanced experimental techniques that can carefully control thermodynamic variables. Conductivity and complex impedance measurements linked to physical properties such as porosity, permeability, and acoustic velocity in porous, water-saturated crustal rocks should also be collected.