The two types of high-sulphur coals Mequinenza and Illinois No. 6, in the initial form and subjected to potassium/liquid ammonia reduction, were analysed by atmospheric pressure-temperature programmed reduction (AP-TPR) method. It has been shown that preliminary demineralisation was beneficial for AP-TPR measurements because of the removal of calcium compounds. The reduction of sulphides and disulphides in the potassium/liquid ammonia system was found to lead to formation of aromatic and aliphatic thiols. The presence of the latter is better manifested in the AP-TPR kinetograms when the measurements are performed in the presence of a special reducing mixture. It has been shown that the coal reduction in the potassium/liquid ammonia system apart from transformations of nonthiophene sulphur groups also leads to breaking up of the C-S bonds in some thiophene systems. (C) 2003 Elsevier Science Ltd. All rights reserved.