The dynamic behavior of inviscid fluid contained in horizontally accelerated cylindrical and rectangular tanks is considered. Mathematical equations describing the fluid motion are developed and simplified by use of small-amplitude wave approximations, enabling expressions for free-surface displacements, pressure distributions and resultant forces and moments on the tank to be obtained. The expressions are formulated in such a way that time-histories of salient parameters can be calculated for tanks subjected to real earthquake accelerograms. Comparisons of predicted and measured free-surface displacements of a model cylindrical water tank subjected to both sinusoidal and seismic accelerations on a shaking table indicate close agreement between theory and experiment. Finally, the solutions for seismic accelerations in one horizontal direction are generalized to include acceleration components in all three coordinate directions.