The Canning Basin is a large sedimentary basin with an onshore area of 430 000 km2. It has a thick, discontinuous succession of Palaeozoic and Mesozoic marine and continental sedimentary rocks covered by Cainozoic surficial sediments. It contains several Zn-Pb sulphide deposits of Mississippi Valley type, mainly in the Lennard Shelf and along the Admiral Bay Fault. To provide a framework for understanding the mechanism of this mineralisation, we made a reconnaissance study of the Palaeozoic aquifers, based on an analysis of data from 30 oil exploration wells. The major Palaeozoic aquifers in the basin are the Early Permian Poole Sandstone, the Late Carboniferous to Early Permian Grant Group, and the Devonian Tandalgoo Sandstone. These aquifers have a complex structure owing to tectonic and erosional effects, and they are interconnected with the younger and shallower aquifers. The general direction of groundwater flow in the Palaeozoic aquifers is from the southeast toward the west and northwest. Groundwater velocity is in the range of 0.2 to 0.5 m y-1, and temperature ranges from 30 to 83°C, Groundwater salinity is low at the margins of the basin, but increases with depth and along the flow lines . Our study suggests that the present hydrogeological regime is basically different from those active in the Silurian to Permian, the interval during which the Zn-Pb deposits are considered to have formed. Compaction-driven and gravity-driven fluid-flow models for the formation of the Zn-Pb deposits are considered. A geopressured zone encountered in one location is evidence that the ore-forming fluids could have been generated in deeper parts of the basin, and expelled by compaction into shale-enclosed sandstone lenses. These geopressured lenses could subsequently have been faulted, and the potential ore-forming fluids released. There is insufficient information on the tectonics, palaeotopography, and age of the mineralisation to assess the gravity-driven fluid flow-modeL