Underground coal gasification (UCG) is a transient and evolving phenomenon in which many chemical and physical changes occur simultaneously and/or sequentially in various regions throughout the coal seam. Heat affected zones of dry and volatile depleted porous zones are formed up to a certain depth of the coal block leading to coal spalling. In the present work, we present a proximate analysis of the coal samples from various locations of the heat-affected zone (HAZ) during borehole combustion and gasification studies which simulate experimentally underground coal gasification. Results from HAZ studies of wood and four coals show that there is a considerable change in the volatiles to fixed carbon ratio in the depth direction and that the extent of variation depends on the coal as well as on the conditions prevailing during the experiment. These results have a potential bearing on the reactivity of the coal and the product gas composition. (C) 2014 Elsevier Ltd. All rights reserved.