During the last years, power utilities in Europe have been changing their feedstocks from indigenous coals to fuels imported from other continents. Many of these coals belong to the so called Gondwana continent and have petrographic and technological characteristics quite different of the ones of the coals of the Northern Hemisphere. These differences are mainly related to the higher proportion of 'inert' components and its reactivity. The coals, in the power stations, are not burned alone but blended in different proportions and the coal blends usually behaves different to the isolated constituents. In this context, this project is aimed to relate the optical properties of the inertinite with its reactivity in combustion processes, to asses the behaviour of the inertinite in coal blends and to establish a quick, easy and inexpensive method to determine the reactivity of the inertinite. The knowledge gained as to the influence of coal depositional setting on inertinite reactivity will provide an initial reference to estimate the inertinite reactivity of coal formed in similar conditions.