The solubility of the single gases hydrogen and carbon monoxide in the ionic liquid 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][CH3SO4]) was measured with a high-pressure view-cell technique based on the synthetic method. The temperature ranged from similar to 293 to similar to 413 K, and the pressure reached up to similar to 9.3 MPa. The gas molality amounted up to similar to 0.1 mol per kilogram of [bmim][CH3SO4]. Carbon monoxide showed a slightly better solubility than hydrogen. The (extended) Henry's law was successfully applied to correlate the solubility pressures. The final results for the Henry's constant (at zero pressure) of hydrogen and carbon monoxide in [bmim] [CH3SO4] (on the molality scale) are correlated within the estimated uncertainty (+/- 1%) by In (k(H.H2)((0))/MPa) = 3.074 + 602/(T/K) and In (k(H.H2)((0))/MPa) = 5.3377 - 66.85/(T/K) - 0.0019517(T/K), respectively. (c) 2006 Elsevier B.V. All rights reserved.