The degree of coalification is an essential parameter influencing the quality of coal reserves. Modelling of the development of this parameter in the Czech part of the Upper Silesian Coal Basin (Carboniferous, Mississippian to Pennsylvanian - Lower Namurian to Westphalian A) revealed the distribution of coalification within the basin in all its stratal units. The grade of coalification was found in principle to be similar but its intensity in general decreases upwards into the hanging wall. Because of different areal extents of individual stratal units the degree of coalification is demonstrated on the oldest and areally most extensive unit - the Petrkovice Member. The studies and their results presented in this paper are based on More than 29,000 analyses of the dry and ash-free volatile matter (V(daf)) in coal samples from surface and underground boreholes drilled in the years 1946-2000. Three zones of enhanced coalification were distinguished: the Ostrava-Pribor Zone, the Roznov-Frenstat Zone and the Pribor-Tesin Zone. These zones were found to correlate fairly well with the occurrence of gas deposits confined to the weathered Carboniferous rock massif or its mantle. Consequently, the degree of coalification does not only determine the quality of coal reserves but may also be used as an auxiliary tool in the search for gas deposits in coal basins. (C) 2009 Elsevier B.V. All rights reserved.