Design and description of a compaction apparatus used at the University of Southern California's Petroleum Engineering Laboratories are presented by the authors. The triaxial loading pressure is changed by varying the liquid pressure of a non-petroleum hydraulic oil around a rubber-sleeved cylindrical core sample. Core samples 1-/ in. in diameter and 2 to 3 in. long can be compacted. The pore pressure of the interstitial fluids is measured by means of a pressure bellows. The pressure vessel and the associated parts are housed inside an electric oven. The loading pressure can be varied from atmospheric to 40,000 psig, whereas the temperature can be changed from room temperature to 212 degrees F. Sample calculations for determining the compressibility and void ratio of a poorly consolidated sand core are presented.