Rarely described until recently, fluid inclusions with H2S as a major component have been studied in various samples of quartz, fluorite and calcite. The phase behaviour at low temperatures of H2S-bearing inclusions (sometimes containing solid S or C) and previously analyzed with the Raman microprobe, is presented. The temperatures of the phase changes are compatible with phase diagrams for the systems CO2-H2S and CH4-H2S, as well as temperature conditions for clathrates formation. Simple thermochemical calculations indicate that in the presence of solid carbon and liquid water, only CH4 + H2S or pure H2S fluid inclusions may be stable at room temperature ; CO2 + H2S + CH4 mixtures are metastable ; the fact that they actually exist could be explained by a very low reduction rate of CO2 at 25 °C.