The high-pressure solubility of hydrogen gas in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)amide ([emim][Tf2N]) was measured experimentally in an equipment based on the synthetic technique. Measurements were carried out within a temperature range of 310-450K and pressures up to 15 MPa. Hydrogen solubility was shown to be low in this ionic liquid, reaching a maximum concentration of about 6 mole percent at the highest temperatures and pressures investigated. Hydrogen solubility showed an "inverse" temperature effect, indicating increased solubility at higher temperatures in contrast to other commonly investigated gas solubilities in ionic liquids, such as carbon dioxide. Within the temperature and pressure range investigated, solubility isotherms on a pressure-concentration diagram approximated linear behaviour. It was also shown that the solubility of hydrogen increases as the alkyl side chain of the cation increases in size within the homologous family. (C) 2012 Published by Elsevier B.V.