Ultrasonic P and S wave Q values as functions of hydrostatic pressure are presented for the Berea and Navajo sandstones, Bedford limestone, and Colorado oil shale. In most cases the attenuation was obtained for both dry and water-saturated samples. Q is determined by measuring the attenuation of the rock sample relative to a high Q standard of identical geometry using Fourier spectral ratios. The data show that Q increases with pressure, the rate of increase being dependent on rock type and crack density and distribution. Qs is about equal to or larger than Qp for dry rocks and less than Qp for saturated rocks. In all cases, Q for saturated rocks are lower than for dry samples. The attenuation in the oil shale shows extreme anisotropy.