01-08U

The phase behaviour of fluids in porous media is studied. The system is described by means of the party quenched model and the replica method is used in order to obtain a grand partition function of a corresponding fully equilibrium system. For an equilibrium multi-component continuous system a functional of the grand partition function given in the phase space of "field" variables conjugated to "density" variables is obtained. In the Gaussian approximation the expressions for a grand thermodynamic potential and chemical potentials as well as the gas-liquid critical point are found. The analysis of the higher approximation implies the possibility of the two phase transitions in a fluid absorbed in porous media. However, this result is not a final one and needs further consideration.