Explosion-induced particle velocity time histories have been recorded in Nugget sandstone at confining pressures between 0.1 and 34.5 MPa using explosive sources with energies 0.6 and 300 kJ. The measured peak particle velocities and peak displacements are insensistive (within the experimental scatter of ¿3%) to confining pressures. Smaller cavities are produced at higher confining pressure, but this reduction in cavity sizes can be attributed to increasing rock strength with confining pressure rather than to confining pressure per se. The recorded free field motion shows a strong departure from elastic behavior, giving average Q or attenuation factors between 8 and 20. Integration of the measured particle velocities to determine permanent displacements gives values an order of magnitude larger than expected from the measured cavity size. This observation suggests that the stress wave causes significant dilation of the rock near the the explosion as it travels outward from the spherical energy source.