Abstract: A natural CO 2 reservoir system with a sandstone lithology in NW Hungary has been studied due to its similarities to a large saline reservoir formation that is widespread in the the Pannonian Basin (Central Europe) and is suggested to be one of the best candidates for industrial CO 2 storage. A range of analytical techniques has been used on core samples from CO 2 -containing sandstone layers that represent a wide range of pressures (90–155 bar), temperatures (79–95°C) and pore fluid compositions (total dissolved solids between 18 000 and 50 700 mg l −1 ) to identify the mineralogy and textural characteristics of the natural reservoir. The only clear CO 2 -related feature in the studied lithology was the occurrence of dawsonite (NaAlCO 3 (OH) 2 ) in a close textural relationship with albite. This is in clear agreement with our geochemical modelling results, which also underline the presence of albite as a precondition for the crystallization of dawsonite at the given P – T – X conditions. Our results suggest that, at least in the Pannonian Basin, dawsonite may be an important mineral for the safe sequestration of industrial CO 2 in the subsurface.