High-pressure compaction studies (up to 200,000 psi) were conducted on kaolinite, illite, and montmorillonite clays and a natural organic colloid of Iranian origin, gum tragacanth. The remaining moisture content in per cent (dry weight) was plotted versus the logarithm of pressure in psi. For kaolinite clay there is a straight-line relationship between 40 and 200,000 psi (M = 33.9 - 5.96 log P), and for illite clay the relationship between the moisture content (per cent) and pressure (psi) can be expressed by the formula M = 50 - 8.7 log P. For montmorillonite clay, on the other hand, there is a break in the curve at about 1,000 psi, and from 1,000 to 200,000 psi the curve is a straight line: M=104 - 18.06 log P. For gum tragacanth, moisture versus pressure curve has a "h perbolic" shape; and it appears to be harder to squeeze water out of the crystalline clays than it is from the amorphous gel at low pressures. The moisture versus pressure curves of the more plastic (higher swelling) clays have steeper slopes than those of the clays having low plasticity; however, much longer time is needed for the establishment of equilibrium in more plastic clays.