The leak-off test (LOT) procedure has been examined within the theoretical framework pertaining to hydraulic fracturing stress measurements (HFSMs). LOT records have then been compared with the results of HFSMs where both measurements have been made in the same boreholes. From this comparison, we make recommendations on the use of LOT data, and suggest a new method of estimating the minimum horizontal stress magnitude () from LOT pressure/volume plots. In-situ stress magnitudes have been investigated by applying these methods to data from over 1000 LOTs in North Sea boreholes. The results of this investigation imply that tectonic stress increases significantly with depth in some parts of the North Sea. which is consistent with the mapped distribution of borehole breakouts.