A data-constrained modelling (DCM) approach with multi-spectrum synchrotron X-ray CT has been used to characterise the physical structure of Yangquan coal sample. Three sets of X-ray CT data have been acquired with monochromatic beam energies at 14, 18, and 30 keV respectively. A DCM approach is used to derive compositional volume fractions on each voxel, by minimising the differences between the expected and CT reconstructed absorption coefficients with a nonlinear optimization algorithm. Voxel based 3D compositional maps are generated with colours and intensities representing compositions and volume fractions respectively. The results are relevant in quantitative modelling of coal-bed gas transportation and coal processing. (C) 2012 Elsevier Ltd. All rights reserved.