Several coals, varying in the coking pressure they generate, were selected in order to study the coal properties influencing the escape of volatiles from carbonising coal charges. The aims of the work were to contribute to the understanding of the mechanism of internal gas pressure generation and to help identify dangerously coking coals. Volatile matter release rates from coal/sand mixtures and from packed coal beds were studied to assess whether gases could be trapped within fused coal beds. Also, the variation with temperature of the rate of volatile matter evolution and degree of Gieseler plasticity were compared to ascertain whether excessive pressures could be identified with high volatile release rates occurring when specific plastic properties were evident. It was found that the internal gas pressure generated by coals, when carbonised in a small double-wall oven, could be related to data obtained by plastometry and thermogravimetric analysis.