In consideration of the rising crude oil and natural gas prices the use of biogases becomes more and more important for the energy supply worldwide. Typically gases produced from bio-resources consist of high amounts of carbon dioxide and sulphur components besides the burnable gas methane. To establish these biogases in the traditional energy systems of the countries, separation techniques have to be used to remove the inert carbon dioxide and the polluting gases. In literature it is already known, that ionic liquids are sorbens, which can be tailor-made for separation processes. Alkyl sulphate and imidazolium-based ionic liquids are for example very suitable for sorption of carbon dioxide [1]. For the engineering of such gas separation processes sorption isotherms are necessary not only for low pressures but also for pressure ranges where typically natural gas is handled. In this contribution a new experimental technique is presented to measure directly the selective sorption of gas mixtures up to high pressures. For these measurements a method is used which combines the volumetric and gravimetric sorption measuring principle together with a high performance sorptiv gas analysis using fluid density and gas chromatographic measuring technique. (C) 2007 Elsevier B.V. All rights reserved.