The paper investigates the effect of self-heating, wetting and freezing of different milled peat types on field storage losses. It has been found that the loss of organic matter in peat due to self-heating depends on peat decay degree, type of product obtained, heating temperature (storage duration), preventive measures taken and the technological scheme of peat extraction. When such preventive measures as moving stacks, internal sealing and compaction of peat are taken, a decrease in self-heating and spontaneous combustion losses is observed. In two-stage harvesting, these losses are lower because of peat compaction in stacking operations. It has been established that there is a dependence of peat losses on its wetting and freezing, storage duration, and the total amount of precipitation accumulated over a certain period. With an increase in peat decay degree, the maximum wetting and freezing losses are several times lower than self-heating losses. These losses are 20% higher for upland peat than for lowland peat.