Experiments on cordierite saturation with “dry” methane, ammonia and the components of H2O-CH4 and H2O-NH3 binary mixtures were performed at 50, 150, 200 MPa in the temperature range from 400 to 800°C to examine the possibility of using Mg-cordierite as an indicator of fluid regime in mineral genesis. We checked that the starting product was free from fluid components at the sensitivity level of the IR and chromatographic methods. Powders with particle size 25–50 μ were used. The run time was 300 h in all the experiments. The typical bands observed in the IR and Raman spectra demonstrate the presence of fluid molecules in the channels. The partition coefficients of CH4, NH3, and H2O between the fluid phase and Mg-cordierite are temperature independent according to the mass spectrometry data. In “dry” systems, small quantities of H2O (up to 0.6 mol.%) are formed by reactions between ammonia and the framework oxygen of the cordierite structure. Thus, the occurrence of water in the structural channels of cordierite does not always mean that water is present in the fluid.