The current work intends to fill a gap regarding physical properties that are relevant for processes using ionic liquids (IL) at elevated pressures and temperatures. As such, the interfacial tension is an important quantity for the behaviour of multiphase systems, e.g. when mass transfer takes place across the boundaries of drops and bubbles. By dissolving within the liquid phase, most gases reduce the interfacial tension. In case of the investigated IL the interfacial tension is decreased in compressed carbon dioxide (CO2) from values of 40-50 mN/m at atmospheric pressure down to 10 mN/m. This order of magnitude is placed between values obtained in the case of water and those obtained for hydrocarbon liquids (oils). Temperature and pressure related densities were retrieved from known equations after finding that the sorption of CO2 into the IL and subsequent density alteration takes orders of magnitude longer than the drop age chosen for the actual measurements. (C) 2009 Elsevier B.V. All rights reserved.