This study investigates the feasibility of storing hydrogen (H₂) and carbon dioxide (CO₂) in a depleted hydrocarbon reservoir (DHR) for geo-methanation, a process that converts H₂ and CO₂ into methane (CH₄). The field trial involved injecting a mixture of natural gas and H₂ into the Lehen DHR over 96 days, followed by a 112-day shut-in period, and then withdrawing the gas over 76 days. After 285 days, 84.3% of the injected H₂ was recovered, indicating the technical feasibility of H₂ storage in DHRs. Laboratory experiments using reservoir-mimicking mesocosms demonstrated that H₂ and CO₂ can be converted to CH₄ at a rate of 0.26 mmol l⁻¹ h⁻¹ over 357 days, equivalent to 114,648 m³ of CH₄ per year (~1.08 GWh). The study also found that methanogens, particularly hydrogenotrophic methanogens, were responsible for the geo-methanation process, as evidenced by stable isotope analysis and molecular methods. The results suggest that DHRs can serve as effective large-scale geo-methanation sites, providing a storable energy carrier compatible with existing infrastructure, and potentially contributing to a net-zero carbon emissions future.This study investigates the feasibility of storing hydrogen (H₂) and carbon dioxide (CO₂) in a depleted hydrocarbon reservoir (DHR) for geo-methanation, a process that converts H₂ and CO₂ into methane (CH₄). The field trial involved injecting a mixture of natural gas and H₂ into the Lehen DHR over 96 days, followed by a 112-day shut-in period, and then withdrawing the gas over 76 days. After 285 days, 84.3% of the injected H₂ was recovered, indicating the technical feasibility of H₂ storage in DHRs. Laboratory experiments using reservoir-mimicking mesocosms demonstrated that H₂ and CO₂ can be converted to CH₄ at a rate of 0.26 mmol l⁻¹ h⁻¹ over 357 days, equivalent to 114,648 m³ of CH₄ per year (~1.08 GWh). The study also found that methanogens, particularly hydrogenotrophic methanogens, were responsible for the geo-methanation process, as evidenced by stable isotope analysis and molecular methods. The results suggest that DHRs can serve as effective large-scale geo-methanation sites, providing a storable energy carrier compatible with existing infrastructure, and potentially contributing to a net-zero carbon emissions future.