Ten linear combinations of the fundamental material constants of electroelasticity and electrostriction of quartz have been determined. They were obtained by the least‐squares fit to 134 observations of the change in the resonance frequency of the thickness modes of quartz plates caused by a dc field. With one exception, there is very good agreement between our results and their counterparts obtained independently by the transit‐time method (pulse propagation in bulk quartz). The differences between comparable constants are no longer out of proportion with their standard errors. This work supersedes earlier results [J. Appl. Phys.65, 715 (1989)].