Hydrogen (H 2 ) will play a key role in low-carbon energy transitions, and it is vital to implement hydrogen storage technologies to enable its safe and economic use at industrial scale. Underground hydrogen storage (UHS) in porous media such as aquifers, depleted hydrocarbon fields, and coal seams has been proposed as widely available long-term and large-scale storage options (Iglauer et al., 2021;Muhammed et al., 2022). As for underground natural gas storage (UGS), UHS involves cyclic gas injection at peak supply (known as cushion gas) and withdrawal at peak demand (working gas). Despite the increasing attention to the topic worldwide, the fundamentals of multiphase hydrogen flow in porous media are still not well described. In particular, relative permeability hysteresis has not been addressed, although its impact has been previously assessed for UGS and CO 2 storage (Colonna et al., 1972;Juanes et al., 2006). The cyclic nature of the UHS suggests that distinct relative permeability functions must be implemented for hydrogen injection (drainage) and withdrawal (imbibition).Relative permeability is a crucial input parameter for the UHS numerical modeling at field scale (Kanaani et al., 2022;Lysyy et al., 2021;Wang et al., 2022). Laboratory gas-water relative permeability curves often have low endpoint gas saturations (<65%) and relative permeabilities (<40%) due to the rock heterogeneity, capillary end effects, gravity segregation, and/or maximum experimental capillary pressure (Krevor et al., 2012;Muller, 2011). Numerical and/or analytical methods are therefore required to validate and extrapolate relative permeabilities in a wider saturation range.Hydrogen-water relative permeability measurements are scarce in the open literature. Steady state drainage experiments resulted in low endpoint gas saturation (∼60%) and relative permeability (∼4%) (Yekta et al., 2018). The authors used experimental capillary pressure to analytically expand the relative permeability curves to higher