New measurements of seismic velocity and attenuation have been made in the kiloHertz frequency range to temperatures of 120 ¿C, confining and pore pressure to 200 bars in Berea sandstone. With increasing temperature, shear velocity and attenuation decrease at all pressures in a fully saturated rock. The data suggest that thermal relaxation is not a significant loss mechanism under these conditions. We propose that dissipation is controlled by a viscous fluid flow mechanism, in which a sharp frequency peak in attenuation is shifted from 2kHz at room temperature to 8 kHz at 120 ¿C as the pore fluid viscosity is decreased with increasing temperature. However, the velocity decrease is too great to be accounted for by a change of relaxation times. A non-dispersive temperature softening in shear may control the velocities.