We study thermodynamically the behaviour of PdSe2 while subjected to high pressure under isothermal conditions. The present paper discusses the volumetric-level calculations and results. Experiments under two certain temperature levels are performed: 20oC and 300oC. Calculations and analyses are done according to the method for thermodynamical analysis developed by us in . We detected the order of phase transition from PdS2 structure type to pyrite one to be first order notwithstanding the temperature level. Values of transition pressure were found to be 12.24 GPa and 9.785 GPa at 20oC and 300oC, respectively. Adjusted entropy generation during compression was calculated aiming to study stability of treated compound. Influence of compression temperature level was analysed, as well as duration of pressure plateaux.