Existing 3D geological systems are well adapted to high data-density environments, such as at the mine scale where abundant drill core exists, or in basins where 3D seismic provides stratigraphic constraints, but are poorly adapted to regional geological problems. There are three areas where improvements in the 3D workflow need to be made: in the handling of uncertainty; in the model building algorithms themselves; and in the interface with geophysical inversion. All 3D models are under-constrained, and at the regional scale this is especially critical for choosing modelling strategies. The practice of only producing a single model ignores the huge uncertainties that underlie model-building processes, and underpins the difficulty in providing meaningful information to end-users about the inh erent risk involved in applying the model to solve geological problems. Future studies need to recognize this and focus on the characterization of model uncertainty, spatially and in terms of geological features, and produce plausible model suites, rather than single models with unknown validity.