This work presents the effect of hydrogen sulfide gas on the phase behavior of both methane gas hydrate formation and CO2 gas hydrate formation. For this, the thermodynamic equilibrium conditions for various gas mixtures containing CH4/H2S and CO2/H2S are initially found by simulation using PVTSim software. These simulated results are compared using an experimental approach and the available literature. Then, the thermodynamic equilibrium conditions generated by simulation are used for generating Hydrate Liquid-Vapor-Equilibrium (HLVE) curves to understand the phase behavior of gases. Further, the effect of hydrogen sulfide on the thermodynamic stability of methane and carbon dioxide hydrates was studied. It was clearly observed from the results that an increase in H2S composition in the gas mixture decreases the stability of CH4 and CO2 hydrates. © 2023 The Authors. Published by American Chemical Society.