Heats of pyrolysis of four Finnish peats were determined by differential scanning calorimetry (d.s.c.), and combustion enthalpies were compared by differential thermoanalysis (DTA) in an air atmosphere. Weight loss data obtained by thermogravimetric analysis (TGA) were combined with the enthalpy data. The heats of pyrolysis of the peats varied between 120 and 250 kJ kg−1. These values were used to model the combustion and pyrolysis of small peat particles (typical in pulverized fuel combustion) and large peat particles (typical in grate combustion). TGA and DTA together gave useful information about the reactivity of peat in an oxidizing atmosphere with changing temperature, despite the similar shapes of the derived TGA (DTG) and DTA-curves. The pyrolysis and combustion behaviour of the peat with the lowest degree of decomposition was similar to that of cellulose, and the differences in the peats were apparent with all the methods used (d.s.c., DTA and TGA). The initial temperatures of pyrolysis and combustion were lower with peats of high ash content (inorganic material) and the combustion proceeded through more steps than with the peats of low ash content.