Inverse Gas Chromatography (IGC) provides a powerful tool for assessing the surface energy of powders by using different chemicals as probes. Finite Dilution Inverse Gas Chromatography (FD-IGC) allows surface energy measurements in a range of probe surface coverages. For heterogeneous materials the relationship between measured surface energy and surface coverage provides information about the surface energy distribution of the material. However, existing methods of analysing FD-IGC data to determine surface energy distributions are based on inappropriate assumptions. Alternative analysis techniques do not determine the material's surface energy distribution but instead provide information about variations in probe-substrate interactions rather than true material properties of the substrate. A more robust method for computing the surface energy distribution of heterogeneous powders is needed. In the pharmaceutical industry, due to the heterogeneous nature of crystalline powders, the surface energy and its distribution plays an important role in the performance of dry powder inhalers, powder mixing, and the cohesion of compressed tablets. Here a new approach for interpreting IGC data, based on more realistic thermodynamic assumptions, is proposed. Using this approach the surface energy distribution of the substrate is determined by fitting the results of simulated experiments to experimental IGC data. The simulation-fitting approach is demonstrated for mannitol and lactose powders. The addition of fines to coarse lactose powder is shown to have a clear effect on the powder's surface energy distribution whilst the surface energy distributions of different particle size fractions of mannitol do not show significant differences in their surface energy distributions. (C) Koninklijke Brill NV, Leiden, 2011