The influence of total pressures and partial pressures of carbon dioxide on the reaction between SO2 and large particles of limestone was studied. The experiments were conducted in a laboratory fixed-bed reactor made of quartz at temperatures up to 950°C, total pressures up to 10 bar, and carbon dioxide partial pressures up to 2 bar. Two types of limestone were tested. At carbon dioxide partial pressures exceeding the calcination equilibrium pressure of limestone, the ultimate degree of sulfation was significantly lower at 850°C than at 750°C, most probably due to sintering of the calcium carbonate. Partly sulfated particles were less sensitive to heat treatment than unreacted and uncalcined limestone. Under calcined conditions, a considerable increase in the ultimate degree of sulfation at 850°C was observed with both types of limestone. A part of the explanation may be the high melting point of CaO compared to CaCO3, resulting in a much slower sintering rate. At 950°C the limestone calcines in the pressure range studied and a relatively high ultimate degree of sulfation was achieved.