The free energy of the hydrophobic hydration and the strength of the solvent-mediated attraction between hydrophobic solute molecules, in the pressure-temperature plane, were calculated. An exactly soluble model, that was an extension of the lattice model was proposed. The mechanism of the hydrophobic effect dominant at low temperature and the opposite mechanism of solvation appearing at high temperatures and has the pressure as a second thermodynamic variable, were taken into account by the model. The two boundaries were identified in the pressure-temperature plane, with this model. It was shown that the first one within which the solubility, or the Ostwald absorption coefficient, decreases with increasing temperature at fixed pressure.