Samples of a German brown coal were treated with acetone-water and methanol-water mixtures of different compositions and the consequent coal swelling was measured. Owing to the very high solubility parameter of pure water, these mixtures have higher solubility parameters than binary organic solvent mixtures commonly used in such experiments. The results are interpreted on the basis that matching of coal and solvent solubility parameters maximizes swelling, although note is also taken of supplementary effects including those accompanying entry of solvent into the coal pores.