Abstract The high pressure phase behavior of a binary mixture containing hydrogen (H2) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) is studied by measuring bubble-point pressures at different temperatures for three compositions with hydrogen mole fractions of 5, 7.5 and 10mol%. Since this work is part of a study to design a hydrogenation process, using [bmim][BF4] as the reaction medium, the effects of adding carbon dioxide (CO2) or the hydrogenation catalyst (−)-1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (cyclooctadiene)rhodium(I) tetrafluoroborate (Rh-MeDuPHOS) on H2 solubility in [bmim][BF4] was measured as well. All measurements were conducted in an autoclave set-up, allowing pressures up to 60MPa and temperatures ranging from 313.15 up to 368.15K. Results indicated that the presence of catalyst increased the H2 solubility in [bmim][BF4] compared to those of binary mixtures of H2+[bmim][BF4] throughout the whole temperature range studied. However, the addition of CO2 to the binary system of H2+[bmim][BF4] increases the H2 solubility at lower temperatures (<330K), and decreases it at higher temperatures (>340K).