The paper presents the results of investigation of organic sulphur occurrence in the coal of Upper Silesian coal basin. Six hundred coal samples from 52 mines were tested. It has been found that the content of organic sulphur in the coal depends on the stratigraphic layer, coalification grade and geographic location in the Upper Silesia region. The highest mean content of organic sulphur has been found in the most recent (ca. 0.85%) and in the oldest (ca. 0.5%) strata. The lowest mean contents of organic sulphur have been found in the intermediate strata. In the case of the most recent coals, the content of organic sulphur decreases with increasing of coalification grade. When the carbon content (C-daf) exceeds 82%, the increase of coalification grade causes no further decrease of the mean content of organic sulphur. The share of organic sulphur in the total sulphur is lower in the case of more recent (< 50%) and higher in the case of older coals (> 50%). (C) 2002 Elsevier Science Ltd. All rights reserved.