Shallow marine gas hydrates occurring above the Sulfate-Methane-Interface (SMI) often contain small amounts of H2S beside methane and other hydrocarbons, but the distribution of H2S in these natural samples is not always homogeneous. To learn more about the formation of H2Scontaining hydrates, gas hydrates with different ratios of H2S/CH4 were synthesized under various conditions. The samples were synthesized from ice and water phases, with constant feed gas compositions or controlled changes in feed gas compositions. It turns out that the detailed nature of the synthetic hydrate samples depends on the method of sample preparation. The sample prepared with gas containing small amounts of H2S (1% H2S and 99% CH4) appeared homogeneous in composition, while that prepared in a water-H2S-CH4 system with higher H2S contents was heterogeneous. The samples were analysed with Raman spectroscopy, and differential scanning calorimetry (DSC).