In this work, the fate of mercury in a bubbling fluidized bed combustor working under oxy-combustion conditions has been studied and compared with air combustion. The influence of burning three different rank coals, with sulphur content ranging from 0.65% to 5.17%, on Hg partitioning has been studied. The presence of limestone as sorbent for SO2 capture as well as the concentration of O-2 at the entrance of the combustor were also evaluated. Coal rank does not have a direct influence on coal partitioning. However, sulphur content of the coal is an important parameter to describe not only the high percentage of particle-bound mercury, up to 87%, in presence of limestone but also the prevalence of Hg(O) as the main species in the gas phase when burning the lignite. The O-2/CO2 ratio has little effect on Hg partitioning in experiments carried out in presence of limestone at 925 degrees C (the optimum temperature for sorbent sulphating under oxy-combustion conditions) and little differences are found with air combustion at 850 degrees C (the optimum temperature for sorbent sulphating under air combustion conditions). Percentage of particle-bound mercury shows a maximum at 925 degrees C independently of the coal studied, which it is related with the maximum sulphur retention for each coal at this temperature.