A method of vibration analysis of spherical shells partially filled with a liquid is presented in which the inertial loading of the liquid is taken into account in the form of an added mass coefficient. A simple formula for the added mass coefficient is derived in terms of the indices of he associated Legendre function of the first kind. The method is semi-empirical and is based on experimental findings by holographic interferometry. Satisfactory agreement is found between the numerical results predicted by the proposed method and the experimental ones.