  We address the problem of predicting saturation-dependent electrical
conductivity {\sigma} in packings of spheres during drainage and imbibition.
The effective-medium approximation (EMA) and the universal power law of
percolation for {\sigma} are used, respectively, at higher and low water
saturations to predict the conductivity, with the crossover between the two
occurring at some intermediate saturation Swx. The main input to the theory is
a single parameter that we estimate using the capillary pressure data. The
predictions are compared with experimental, as well as numerical data for three
distinct types of packings. The results for drainage in all the packings
indicate that the universal power law of percolation is valid over the entire
range of Sw. For imbibition, however, the universal power law crosses over to
the EMA at Swx = 0.5. We also find that the effect of the pore-size
distribution on the {\sigma}-Sw relation is minimal during both drainage and
imbibition.
