The hydrostatic properties of the materials methanol, isopropyl alcohol, water, sodium chloride, silver chloride, and the binary mixtures pentane‐isopentane and methanol‐ethanol have been determined in the diamond‐anvil pressure cell up to 180 kbar by line‐broadening and line‐shift measurements of the sharpR1ruby fluorescence line. A liquid mixture 4 : 1 by volume of methanol : ethanol remains hydrostatic to almost 100 kbar at room temperature. This mixture exceeds the hydrostatic limit of the previous generally accepted fluid, 1 : 1 pentane : isopentane which has a hydrostatic limit of about 70 kbar. Silver chloride and water (ice VII) are better than sodium chloride as pressure‐transmitting media, but do not even qualitatively approach hydrostatic conditions much above 70 kbar. The stress sensitivity level of the ruby limits the extent to which slight deviations from hydrostatic conditions can be determined in solid systems and suggests the qualitative nature of the method in characterization of quasihydrostatic states. The equilibrium freezing pressure of methanol at 24°C was redetermined to be 35.8±0.8 kbar.