The differential-normalized method of electrical exploration (DNME), by means of polarization study of the secondary sulphidation zone (depth ~ 0,4-0,6 km), allows making conclusion about existence and parameters of an oil and gas deposit (depth up to ~ 2-5 km). The approximate solution of the system of nonlinear differential equations in partial derivatives for concentration of sulfur-hydrogen and pyrite (polarizability) as the function of oil-gas deposit depth has been received. The results are confirmed by experimental investigations in the North Sea.