A pulse superposition method of determining ultrasonic wave velocities in materials such as single crystals is shown to be well suited to measurements for pressure and temperature variations. With this method the effect of coupling between transducer and specimen can be made negligibly small. Data are presented for longitudinal waves propagated in theXdirection of quartz and forXYshear waves propagated in theYdirection of quartz. Pressure was varied from 1 atm to 30 000 psi at 25° and −195.8°C. Curves for facilitating the measurement of absolute velocities for a range of specimen impedances are shown in the Appendix.