We experimentally determined the maximum tension in synthetic fluid inclusions from the difference between the temperatures of homogenization (T h) and spontaneous vapor nucleation (T n). At temperatures of 100–200°C, liquid water may exist at negative pressures of up to 100–150 MPa. Owing to an increase in surface tension, the effect is even more significant in salt solutions and occurs at higher temperatures. A decrease in the linear dimension of fluid phase by an order of magnitude and, correspondingly, a three orders of magnitude decrease in volume (which is proportional to R 3) increase the maximum tension by ∼25MPa. Tension in the liquid phase of water-salt systems may be higher than ~200 MPa without cavitation. Metastability of water and salt solutions in small-sized vacuoles generates stresses in the fluid-mineral system resulting in high solubilities of solid phases. An increase in volume due to coalescence of small inclusions or vanishing of metastability results in an abrupt decrease in supersaturation.