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Abstract Hydrostatic pressure has a vital role in the biological adaptation of the piezophiles, organisms that live under high hydrostatic pressure. However, the mechanisms by which piezophiles are able to adapt their proteins to high hydrostatic pressure is not well understood. One proposed hypothesis is that the volume changes of unfolding (ΔV_Tot) for proteins from piezophiles is distinct from those of nonpiezophilic organisms. Since ΔV_Totdefines pressure dependence of stability, we performed a comprehensive computational analysis of this property for proteins from piezophilic and nonpiezophilic organisms. In addition, we experimentally measured the ΔV_Totof acylphosphatases and thioredoxins belonging to piezophilic and nonpiezophilic organisms. Based on this analysis we concluded that there is no difference in ΔV_Totfor proteins from piezophilic and nonpiezophilic organisms. Finally, we put forward the hypothesis that increased concentrations of osmolytes can provide a systemic increase in pressure stability of proteins from piezophilic organisms and provide experimental thermodynamic evidence in support of this hypothesis.