Compressibilities of halloysite, hectorite, and illite clays, saturated in distilled water, were determined at pressures ranging from 600 to 34,000 psi. The approximate compressibility of the suspensions ranged from about 5 × 10^-5 to 4 × 10^-6 psi^-1, calculated from the thickness or height (h) versus pressure (p) measurements [c_bh = -1/h(dh/dp)]. The densities of the clay solids were determined after compaction at various pressures. These clay solid densities were found to decrease with increasing compaction pressure. This apparent density variation may be due to a lower density of the remaining water in the clay solids, or to increased amounts of adsorbed or interlayer water ("driving-in" of water effect). Above a spec fic pressure, different for each clay, the compressibilities determined from measured height changes begin to exceed theoretical compressibilities. The theoretical compressibility plots have been previously determined from remaining moisture content versus pressure data, assuming constant clay solid densities.