<p>Understanding gas migration in salt formations is critical for the safe and efficient operation of underground energy storage (UES) systems. This study examines the coupled effects of gas type (He, N₂, CO₂) and confining pressure (5–30&#xa0;MPa) on the permeability of rock salt and interlayer materials using laboratory-scale seepage experiments and core-scale numerical simulations. The results show a significant decline in permeability with increasing confining pressure, especially in halite, where microcrack closure and self-healing mechanisms enhance sealing performance. In contrast, interlayer formations retain high leakage rates due to their fractured and heterogeneous nature. Among the gases, He exhibits the highest leakage rate owing to its small molecular size and high mobility, while CO₂ demonstrates superior containment. The study introduces an m value index to quantify the sensitivity of permeability to confining pressure, enabling cross-comparison among gases and lithologies. Strong correlation (<i>R</i>² &gt; 0.95) between experimental and simulation results validates the modeling framework. These findings reveal how molecular characteristics and geological heterogeneity jointly govern gas transport and provide practical guidance for gas selection, site screening, and sealing design in salt cavern UES systems, with direct implications for hydrogen and CO₂ storage applications.</p>