The generalised single degree of freedom analysis can be used for the fair assessment of buckling possibilities in steel tanks. Present paper deals with exercise made for investigating the tank for the overall (global) buckling considering the generalised single degree of freedom concept with distributed flexibility of the tank wall. Equation of motion is mainly used to derive elastic and geometric stiffness formulations by suitable selection of shape/displacement functions w.r.t. boundary conditions. The possible changes in tank geometry like ovaling and tilting due to settlements/angular distortions are considered for exploring the buckling possibilities of the tank. The liquid mass is considered as impulsive mass where sloshing frequency is considered independently as external forcing frequency. Paper comprises the parametric and comparative study between the tanks of varying sizes with different shape functions for different buckling parameters. Earlier, (A. S. Veletsos: Seismic effects in flexible liquid storage tanks. 5th World Conference Earthquake Engineering, vol. pp. 630–639. (1974)) had used the equation of motion for tanks using generalised single degree of freedom approach. However, it was aimed to calculate overturning moment, base shear and hydrodynamic pressures while in the present work, stiffness are mainly focused in view of the buckling possibilities. It has been observed that tanks are having enough bending stiffness against global buckling, however, variations found in tanks buckling tendency with reference to tank sizes as well as tilting and ovaling.