This review establishes underground hydrogen storage as the linchpin for scalable, clean hydrogen economies. The safe and effective deployment of hydrogen storage relies on a multi-scale understanding of its behavior in the subsurface. It identifies geological storage primarily in depleted hydrocarbon reservoirs and salt caverns as the optimal solution, offering superior energy density, safety, and capacity surface storage methods. Global analysis reveals that 80% of underground hydrogen storage projects use depleted natural gas and oil reservoirs, with over half specifically targeting depleted gas and condensate fields, capitalizing on their cost-effective existing infrastructure. Also, in this study, techno-economic analysis confirms underground hydrogen storage as the most cost-effective option for large volumes. On the other hand, the strategic use of cushion gas (e.g., carbon dioxide, nitrogen, methane) is critical for maintaining pressure and operational efficiency, with gas selection directly affecting environmental risk and compatibility. Generally, this review synthesizes key technical, economic, and policy insights to accelerate the industrial-scale advancement of underground hydrogen storage, a vital technology for climate action.
