New experimental results are presented for the solubility of carbon monoxide in the ionic liquid 1-N-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF6]) for temperatures from 293 to 373 K and pressures up to about 10 MPa. The experimental results reveal nearly no influence of temperature on the solubility of CO in [bmim][PF6]. The ionic liquid [bmim][PF6] is a poor solvent for carbon monoxide; for example, at 9 MPa only about 0.15 mole of the gas are dissolved in 1 kg of the ionic liquid. The (extended) Henry's law is applied to correlate the solubility pressures. (c) 2004 Elsevier B.V. All rights reserved.