Static and dynamic bulk moduli (Ks and Kd) are measured as continuous functions of pressure from zero to 2--3 kilobars for two sandstones, a tuff, limestone, granite, and oil shale. Results for the sandstones and granite are in good agreement with previously reported data with Ks/Kd varying from about 0.5 at atmospheric pressure to close to unity at pressures 2 kilobars and above. For rocks behaving elastically under static loading, the Ks/Kd ratio is inversely related to the microcrack density. For the limestone, time dependent deformation associated with pore collapse results in Ks/Kd ratios approaching 0.1 at high pressure. Upon unloading, while initially high (~1.0) at high pressures, Ks/Kd becomes lower than values obtained during loading at low pressures (<1 kilobar) due to opening of microcracks generated during pore collapse. For the oil shale, in which few microcracks exist, Ks/Kd remains relatively constant with pressure at a value of about 0.7.