The estimation of petrophysical properties (i.e. porosity, lithology, and pore fluids) is commonly done by first estimating rock properties (i.e., S- and P-wave velocities and density) from prestack seismic data. Then by some empirical or theoretical transform, the rock properties are converted to the desired petrophysical properties. There are risks associated with this procedure. Among other things, what sensitivity does a rock property show to changes in petrophysical properties or what is the possibility of having more than one combination of petrophysical properties yielding the same rock-property value (ambiguity)?