The most promising method of coal drying is the high pressure superheated steam drying (HPSHSD). High temperature and pressure sorptional equilibrium of lignite used in HPSHSD design is rarely available. The measurement requires either complex equipment or is time and labor consuming. In this work a novel isochoric method of high temperature and pressure desorption equilibrium measurement is described which uses a standard autoclave and easy to follow experimental procedure. Using this method the desorption equilibrium of low rank coal of Belchatow open pit mine was measured in the range of temperatures up to 200 degrees C and pressures up to 23.6 bar. A BET type equation was fitted to the experimental data with correlation coefficient of 0.960. The results obtained compare well to the results obtained for low rank coal using much more sophisticated equipment. (C) 2013 Elsevier Ltd. All rights reserved.