The observed resistivities of synthetic cores comprising disseminated test lead particles, quartz sand grains, and commercial cement (25% by volume) and saturated with NaCl solutions are apparently best represented by a relationship similar to that of an electrically parallel circuit. The empirical relationship that best approximated the experimental data is: Equation where rho t is the observed resistivity of the core; rho Pb is the resistivity of the lead; F P is the formation factor that the core would have if none of the solid materials were conductive; rho w is the resistivity of the saturating conductive fluid; and alpha is a parameter dependent upon the fractional volume of the fluid (phi w ), the fractional volume of lead (phi Pb ), and other factors. These experiments indicate that alpha can be approximated as follows: Equation where C and K are "constants" for these particular experimental conditions. It was found that the observed resistivity varies markedly with changes in either lead content or the fractional volume of saturating conductive fluid. At low values of the fractional volume of lead, the current conduction through the cores is largely electrolytic, and the observed resistivity is strongly influenced by changes in the fractional volume of the saturating fluid. When the fractional volume of the saturating fluid is maintained relatively constant and the lead content is increased, the observed resistivity decreases because some of the current is conducted through the lead particles by electronic conduction.