The study of the combustion process carried out in an oxygen-enriched atmosphere in a circulating fluidized bed (CFB) combustor is presented. The experiments were focused on fuel behavior in the conditions of increased oxygen concentration, at a different temperature and a different fuel load in the combustion chamber. The tests were performed in a laboratory-scale CFB combustor. Brown coal was used as the fuel. The values of variable parameters were in the following ranges: the oxygen concentration in the delivered stream of gas substrates (mixtures of O-2 + N-2 and O-2 + CO2): 21 divided by 60%; the combustor's temperature: 973 divided by 1133 K; the mass of fuel portions: 4 divided by 8 g. Based on the obtained data, carbon, sulfur and nitrogen conversion ratios were calculated. (c) 2006 Elsevier B.V. All rights reserved.