This paper considers the problem of identifying parameters of oil and water saturated quartzite-feldspar beds from neutron-neutron and neutron activation logs. These beds are similar to a wider class of polymictic ones. The unknown parameters are porosity, partial volumes of water and oil and the mineral constituents. Here, the mathematical model of the problem is presented, a system of equations for determining the parameters is formulated, and a method of its numerical solving is suggested. The efficiency of the approach is supported by results of numerical experiments. In cases when the ill-conditioned nature is essential, the numerical method includes a special regularization procedure. (C) 1999 Elsevier Science Ltd. All rights reserved.