The electrical resistivity of an originally fully water saturated glass bead sample during the process of hydrate formation from methane dissolved in the pore water without a free gas phase was measured. In addition to the sample resistivity we measured the resistivity of the circulating water in order to determine the amount of water consumed by hydrate formation from the increase of salinity and to determine the formation resistivity factor and resistivity index. The resistivity of the sample increased from 5.1 Ωm at 100% water saturation to 265 Ωm at about 95% hydrate saturation whereas the water resistivity decreased from 1.39 Ωm to 1.08 Ωm. The observed dependence of the resistivity index versus water saturation cannot be described with the Archie-equation using a constant saturation exponent, but corresponds to what was predicted by a cubic sphere pack model.