Thermoanalytical techniques have found widespread use as a quality-control tool for petroleum and related products. Pressure differential scanning calorimetry (PDSC) has been effectively used as an alternative method to estimate thermal-oxidation stability of middle-destillate fuels. In this paper, the fuels were rated on thermal stability on the basis of their enthalpy of the exothermic reaction 'Oil + O₂ → Oxidation Products' under isothermal conditions. The thermograms before and after a certain period of time under thermal-oxidative strain have been compared in order to determine the average heat flow during that period and, therefore, to obtain an indication to fuel storage stability. Six heating oils of diverse composition and origin were selected for the investigation. On the basis of these examples a correlation between the physical-chemical properties and the DSC data has been shown and the factors influencing the thermal-oxidation stability have been evaluated. The reliability of the method with regard to predicting long-term storage stability has been discussed.