Determination of nuclear-magnetic properties of rocks at different distances from the borehole [i.e., lateral nuclear magnetic sounding (LNMS)] provides the possibility of enhancing formation evaluation. The LNMS can be performed by a special nuclear magnetic tool operating either in the Earth's magnetic field or in the field of permanent magnets. One of the most important problems that can be solved by means of LNMS is determining the character of the flushedzone radial inhomogeneity, which is, in turn, a function of the saturating fluid and the reservoir's porosity and permeability. Downhole experimental measurements performed using a LNMS tool operating in the Earth's magnetic field proved the possibility of delineating mud-contaminated zones and of distinguishing between gas-bearing and oil- or water-bearing reservoirs. Quantitative determination of the free fluid index (Iff) of shallow and deeper parts of the flushed zone makes determination of the reservoir's porosity and permeability more accurate.