The burn-out of carbon in pulverised fired power stations is commercially important. Interest in the burn-out of biomass chars is growing because biomass is increasingly being co-fired with coal to reduce the carbon dioxide emissions. The significance of carbon burn-out is that it is linked with the efficiency of the plant and the suitability of the coal ash for construction purposes. Residual carbon in ash has generally increased in recent years because of the influence of the lower temperatures and slower mixing resulting from the use of low NO, burners. The amount of unburned carbon is thus a function of the plant design and operating conditions but it is also linked to the ease of combustion of the coal and the char formed. These latter factors are related to the properties of the coal and this paper attempts to quantify the impact of certain coal and char properties on carbon-out. An approach for assessing biomass combustion performance is also discussed. (C) 2003 Elsevier Ltd. All rights reserved.