Desulfurization of Mae Moh coal with supercritical ethanol/potassium hydroxide in a semicontinuous reactor was studied. A two-level factorial experimental design was applied to study the main effects on sulfur reduction. The variables investigated in this work were temperature, pressure, time and potassium hydroxide concentration. The measured responses in the experimental design were coal yield, sulfur reduction and ash reduction. The analysis of the results from the design showed that two variables, temperature and KOH concentration, can be considered to have a significant effect on the pyritic sulfur and total sulfur reduction. (C) 2003 Elsevier Science B.V. All rights reserved.