AbstractThis paper addresses the quality control problem faced by a coal mine of satisfying a specified minimum net calorific value (NCV) requirement for the coal loaded at an export harbour, by means of a control strategy on the gross calorific value (GCV) at the mine's wash-plant. From the NCV:GCV relationship a formula for the target mean GCV at the wash-plant is derived. This takes into account the variation of the GCV from the wash-plant, the joint variation of GCV, hydrogen, total and air-dried moistures at the ship sampler and the minimum NCV requirement specified in the export contract. A Bayesian control strategy is derived whereby the specific gravity of the heavy-liquid medium in the wash-plant is changed in response to deviations in the GCV from its target value. Finally, the theory is used to establish a quality control strategy for an open-cast coal mine.