The effect of dispersion on acoustic wave sensors is considered experimentally. A recent theoretical prediction that the phase velocity mass sensitivity of guided shear horizontal surface acoustic wave devices can be obtained using measurements of phase and group velocity, and that the group velocity is highly sensitive to mass loading, is investigated. Experimental data for a polymer-coated surface-skimming bulk wave device on an ST quartz substrate is presented. Measurements of phase velocity, group velocity, and insertion loss determined by a network analyzer were obtained by systematically increasing the guiding layer thickness. Liquid sensing using poly (ethylene glycol) solutions with increasing densities were performed and phase and group velocities measured. The increase in mass sensitivity With the guiding layer thickness is significant and the data confirms the theoretical prediction that group velocity is a more sensitive parameter than the phase velocity to liquid loading.