Conversion of Xiaolongtan lignite in sub- and supereritical water (SCW) was studied in an autoclave in the temperature range of 350-550 degreesC and water density 0-0.21 g/cm(3) for 0-60 min under N-2 atmosphere. The experiments were carried out to investigate the effect of temperature, water density and reaction time on gas yields, liquid yields and product components. The results clearly indicate that the key factor that affects the product distribution is reaction temperature. Compared with temperature, the influence of water density and reaction time is less significant. To clarify the role of water in conversion of coal, experiments under nitrogen were also carried out. Comparing with the pyrolysis process without water under N-2 atmosphere, conversion of coal is enhanced in the presence of water. (C) 2004 Elsevier B.V. All rights reserved.