Because of some disagreements among published data on the solubilities of gases in ionic liquids, an IUPAC project to establish recommended values for some properties and suggest suitable measurement methods was initiated. As part of this large project, this study focused on the solubility of hydrogen gas in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. High-pressure gas solubilities were measured at various temperatures up to 370 K and pressures up to 12 MPa. The results showed very good agreement between the data measured in this laboratory and those of two other laboratories where the hydrogen solubilities in the same IUPAC sample were measured using differing experimental setups.