Abstract <p>The influence of treatment with various gases on the surface wettability of coal of early and intermediate metamorphic stages is studied. The wettability is assessed by water filtration through a bed of coal powder. For coal samples prepared in air, the filtration rate is higher on account of surface oxidation and greater hydrophobic activity of the contacting layer. The worse filtration properties of coal samples prepared in nitrogen and CO₂ indicate greater hydrophobic activity of their surfaces. The influence of CO₂ and nitrogen on the filtration properties is greater for coal of little metamorphic development, perhaps because of molecular interactions (hydrogen bonds) and chemical reactions (carbonate formation) of the CO₂ molecule with polar functional groups of the coal.</p>