This paper presents the experimental and theoretical investigations of the sorption of water vapour in hard coal samples from Polish collieries (So snica, Jaworzno and Pni owek). Analysis of the sorption isotherm of water molecules gives information on specific interactions with surface groups, especially oxygen radicals. Detailed considerations of experimental results and theoretical simulation estimates let us to indicate changes in the surface composition for the different samples of coals and its dependency on the petrography or metamorphism.