The activity of fluidized bed particles towards the volatile matter of a bituminous coal was analysed by measurement of tar yield and the direct measurement of CO2 concentration in the exhaust gas from the devolatilization of bituminous coal particles in a laboratory-scale fluidized bed reactor. In a third approach, thermogravimetric analysis (t.g.a.) of the fluidizing particles was performed, indicating that calcium-containing particles exhibited the largest weight loss. In a fourth approach, a mass spectrometer was connected to the t.g.a. instrument to identify the gases responsible for the weight loss. The results from the third and fourth approaches are presented in this paper. T.g.a. weight loss profiles of calcium-containing solids under certain conditions were very complex. Mass spectrometric analysis of the effluent gases from particles pre-exposed to the volatile matter of a bituminous coal in a fluidized bed showed that CaSO4 may decompose under reducing conditions due to the presence of combustion intermediates such as CO and H-2, and the presence of oxygen may complete the sulfation reaction. (C) 1997 Elsevier Science Ltd.