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Depleted natural gas reservoirs play an important role as a viable option for large-scale hydrogen storage and production. However, its deployment depends on the accurate knowledge of the cushion gas (such as CH₄, CO₂, and N₂) compositions, which are key components affecting the rock-fluid interfacial phenomenon. In addition, there are currently few reported studies on rock/brine/gas-mixture wettability and gas-mixture/brine surface tension representing this type of reservoir. Hence, we report the feasibility of using CH₄ as a cushion gas (in the presence of CO₂ and N₂) for H₂ storage at various pressures (500 up to 3000 psi), temperatures (30 up to 70) ^oC, and salinities (2 up to 20) wt.% using drop shape analyzer equipment. Contact angle (CA) and surface tension (ST) experiments were extensively conducted for the different gas mixtures (H₂–CH₄–CO₂–N₂) to establish relevant data for H₂ storage in …