The solubilities of CO2 and the liquid densities in a Brensted acid-base ionic liquid, [DMFH][Tf2N], composed of N,N-dimethylformamide (DMF) and bis(trifluoromethanesulfonyl)amide (HTf2N) have been investigated at high pressures and at different temperatures. The results were compared with those in DMF and a typical 1-butyl-3-methylimidazolium analogue with the same anion, [BMIM][Tf2N]. The mole fraction scaled solubilities of CO2 in the three liquids showed a slight increase in the following order, DMF<[DMFH][Tf2N] < [BMIM][Tf2N], whereas more remarkable difference was observed in the volume scaled concentrations of CO2, [BMIM][Tf2N] < [DMFH][Tf2N] << DMF, mainly due to the bulkiness of liquid entities. (C) 2010 Elsevier B.V. All rights reserved.