This study investigated self-heating and of-gassing of Scots pine (Pinus sylvestris) wood pellets made from sawdust generated from separated mature and juvenile wood. The pellets were produced at an industrial scale and stored in large piles of about 7.2 tonnes. The production process involved drying the sawdust using three diferent methods and to varying moisture contents. The results indicated signifcant infuences of both raw material type (F (6)=61.97, p<0.05) and drying method (F (2)=65.38, p<0.05) on the self-heating of the pellets. The results from the multiple regression analysis further showed that both the raw material type and pellet moisture content signifcantly infuenced the temperature increase, with strong correlations observed for pellets produced using low-temperature drying (F (3, 14)=83.52, multiple R2=0.95, p<0.05), and medium temperature drying (F (3, 13)=62.05, multiple R2=0.93, p<0.05). The pellets produced from fresh mature wood sawdust were found to be more prone to self-heating and of-gassing while steam drying the sawdust at high temperature and pressure led to a signifcant reduction in heat and gas generation across all materials. The heightened self-heating and of-gassing in mature wood pellet can be attributed to a higher proportion of sapwood in the raw material. The probable explanations to the observed diferences are in line with biological mechanisms for self-heating and of-gassing, as well as the chemical oxidation of fatty and resin acids.