Methods, systems, devices and products for evaluating an earth formation comprising a porous medium. Methods include estimating at least one property of the earth formation using a plurality of estimates of complex permittivity based on measurements using an electromagnetic tool at a plurality of frequencies in a borehole penetrating the earth formation while the porous medium is saturated with a mixture of water and a plurality of hydrocarbon phases including oil and gas by using a spectral dielectric curve constant (v) for the porous medium, the spectral dielectric curve constant (v) invariant with respect to a ratio of water to hydrocarbons in the porous medium and determined by an estimated rate of change between estimates of the plurality of estimates of complex permittivity of an imaginary part relative to a real part of each estimate.