The Geysers geothermal field is located in northern California and is one of the world＇s largest producers of electricity from geothermal energy. A key resource management issue at this field is the distribution of fluid in the matrix of the reservoir rock. In this paper, we interpret seismic compressional-wave velocity and quality quotient (Q) data at The Geysers in terms of the geologic structure and fluid saturation in the reservoir. Our data consist of waveforms from approximately 300 earthquakes. Using compressional-wave arrival times, we invert for earthquake location, origin time, and velocity within a three-dimensional grid. Using the pulse width of the compressional wave, we invert for the pulse width contribution associated with the source and the one-dimensional Q structure. We find that the velocity structure correlates with known mapped geologic units. The dry steam reservoir, which is known from steam well drilling, is mostly correlated with low velocity. The correlation is best for those areas where the steam pressure has been reduced by production. The Q increases with depth to the top of the dry steam reservoir and decreases with depth within the reservoir. This decrease of Q with depth suggests that the liquid saturation of the reservoir rock matrix increases with depth.