Screen printing has been used to fabricate thick films of various compound and mixed oxides in the Sn-W-O system for gas-sensing studies. The powders for the thick-film pastes were made by heating in vacuum various mixtures of SnO and WO3 powders, corresponding to the nominal formula SnxWO3+x. Here we have studied the mixed oxide system of tin and tungsten with the atomic ratio x between 1.25 and 2.5. Two new semiconducting compound structures (undocumented phases) were synthesized in this composition range between tin and tungsten. A sedimentation method was used for an enrichment 'cleaning' of a particular phase from the fused powders and an analysis of the measured Mossbauer spectra was used to determine the relative amounts of different phases in the powders. Raman spectroscopy together with X-ray diffraction were also used for the structure characterization of the powders and for the identification of the two new undocumented compounds. The gas response properties of thick films made from the two 'cleaned' new compound phases were studied at different temperatures between 100°C and 400°C.