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The highest pressure mercury porosimeters only probe pore-throats down to a size of 4 nm.  However, some materials have void network and pore-fluid properties which are predominantly, or significantly, governed by voids below 4 nm, and pore-fluids within them.  Under such circumstances, it is possible to extend the percolation curve to smaller sizes.  To do that, a very high sensitivity and accuracy surface area analyser is required.  Then, if the surface of the sample is sufficiently well characterised and homogeneous, an equivalent percolation curve can be calculated from the Langmuir adsorption isotherm by matching it to Grand Canonical Monte Carlo (GCMC) simulations (see Jones et al., 2018, and Matthews et al., 2018) .  For heterogeneous nanoporous solids, such as tight-oil shales, GCMC is not possible, and simpler approximations, such as BJH, are unlikely to work.