This paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of Westerly granite. Data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5°–70°C. For 1:1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately −4 mV/(atm Ωm) and for 2:1 electrolytes −2 mV/(atm Ωm). The effect of temperature was small (0.05 mV/°C temperature increase) and indicates that the zeta potential was independent of temperature. Preliminary experimental results using mixed electrolytic solutions (NaCl + CaCl2) and two-phase fluid flow are also described. Two-phase flow can enhance streaming potentials by as much as a factor of 3 or 4. The laboratory data are used to interpret streaming potentials in geological problems, such as earthquake prediction, geothermal prospecting using the self-potential method, and surface conductivity contribution to the electrical resistivity of rocks.