Hydrogen is currently assessed as a future clean fuel in a hydrogen economy. However, one key problem with implementing a full-scale hydrogen economy is hydrogen storage (as hydrogen is highly compressible and volatile). One solution for this problem is hydrogen geo-storage, where compressed hydrogen is injected into geological formations, and the hydrogen can be withdrawn again at any time. However, there is a serious lack of data for realistic geologic conditions, including for hydrogen-rock wettability, which is proven to determine injectivities, withdrawal rates, storage capacities, and containment security. We thus measured this parameter at various geo-storage conditions. For a realistic storage scenario in a deep sandstone aquifer, we found that the rock (quartz) was weakly water-wet or intermediate-wet. Increasing pressure, temperature, and organic surface concentration increased hydrogen wettability. This study, thus, provides fundamental data and aids in the industrial-scale implementation of a future hydrogen economy.