The (beta, gamma) deformation parameters of even-even Xe, Ba, and Ce n
uclei have been calculated by using the triaxial rotor model. Deformat
ion parameters calculated, on one hand, from decay properties and, on
the other hand, from energies are in good agreement. The smooth depend
ence of the deformation parameters on Z and N is discussed. The result
s are compared with those extracted from properties of odd-A nuclei.