Breakouts in four wells in Hudson Bay suggest that the Paleozoic section is currently subject to maximum horizontal compression about a northeast–southwest axis, with some local deflection in horizontal stress orientations related to faults. The Paleozoic section does not appear to be detached from the crystalline basement of the Canadian Shield, despite the presence of thick Silurian halite-rich intervals. The northeast–southwest compressional axis documented in the Hudson Bay Basin is compatible with stress orientations mat have been measured in other parts of cratonic North America. Leak-off tests from three wells imply that contemporary horizontal stress magnitudes above 1500 m depth exceed present-day overburden loads; comparable relative magnitudes have been measured elsewhere in central Canada. Finite-element modelling suggests mat this phenomenon is due to the effects of glacial loading, crustal rebound, and spreading of the Mid-Atlantic Ridge.