A joint project between Dr I.G. Watmuff (consultant) and the Department of Mines and Energy, South Australia, to appraise the soil air CO2/O2 technique as a guide to concealed oxidising sulphides, has been completed. Testing was conducted over known mineralisation in a variety of geological and geographical settings including the Mount Lofty Ranges, Moonta District, Eyre Peninsula, Stuart Shelf and the Olary Block. Encouraging results were obtained from some localities, but generally results were ambiguous due to near surface active soil zones and the shallow sampling depth (75 cm). It is essential that future gas sampling be from 3-5 metres depth, avoiding the active soil zone and any calcrete horizons. It is recommended that orientation studies be undertaken to test the most suitable sampling depth. This would involve shallow drilling, and it is also recommended that drill hole samples be tested for sulphur gases, particularly CS2 and COS, which are also potential indicators of oxidising sulphide.