Measurements and calculations of reflection spectra of an X‐cut LiNbO3 plate immersed in a dielectric fluid have been performed, with the numerical results presented in an innovative image data format. The influence of dielectric fluid loading on all branches of the reflection coefficient function has been investigated. Strong piezoelectric coupling leads to unexpected plate wave dispersion in the fundamental symmetric mode, where the group velocity exceeds the phase velocity at low frequency. The experimental data are in excellent agreement with the results of an exact partial wave analysis. These phenomena and their effect on plate wave behavior can play an important role in the performance of chemical or physical liquid sensing devices.