Seismically induced bending moments in the walls of rectangular concrete liquid storage tanks are evaluated. The tank is assumed to be subjected to simultaneous horizontal and vertical components of earthquake excitations. The liquid is assumed to be homogeneous, inviscid, and incompressible. Hydrodynamic pressures are calculated using the classical potential flow approach and are compared with those obtained from approximate analyses. Typical systems of loadings are identified and applied on the walls which are assumed to behave as elastic plates. Analytical expressions for the computation of internal moments are presented, and numerical values of moment coefficients are tabulated for use in seismic design analysis of tank walls.