The Z-1/11 and Z-2/12 drillings are located north of the closed „Morcinek” coal mine – situated near Cieszyn, close to the Polish-Czech border (Fig. 1). The coal seams in the area are found in Carboniferous coal-bearing formations within the north-western part of the main basin, which is the central part of the Upper Silesian Coal Basin. The profiles of examined drillings included the samples of coal occurring in 11 intervals in the Z-1/11 drilling and 14 sections in the Z-2/12 drilling (Fig. 2). Petrographic studies of coal seams from the Z-1/11 and Z-2/12 drillings allowed to identify the rank of coal on the basis of reflectance measurements. Random reflectance (Ror) of collotelinite in the Z-1/11 drilling is 0.81%, while in the Z-2/12 drilling it is 0.84%. Measured values indicate similar coal rank in both drillings, which corresponds to – according to Polish standard PN-82/G-97002 – gas coal type 33. According to the International Classification of In-Seam Coal, and therefore on the basis of petrographic composition, the coal from both boreholes has been identified as humic coal. On the basis of the rank of coal, measured using the random reflectance (Ror), the coal has been identified as medium-rank C (ortho- bituminous). In terms of ash content, coal from the individual seams has a very high variability, ranging from high grade coal through medium-low-very low grade coal up to carbonoceus rock. [...]