Four tanks, from 6 inches to 4 feet in diameter, have been subjected simultaneously to transient, horizontal “ground motions” of simplified type. The important parameters, in addition to size of tank, were depth of fluid and frequency, duration, and amplitude of ground motion. The envelopes of the gravity-wave profiles have been recorded on a vertical plane of symmetry placed within each tank in a direction parallel to the ground motion. The data include samples of the wave envelopes, photographic studies of the wave formation, maximum wave heights and the locations of these maxima, and the fluid damping coefficients. Equivalent mass and overturning moment due to the fluid have been shown for various degrees of confinement of the upper surface, from complete confinement (owing to use of a rigid cover) to a free surface. The study relates to the effect of earthquakes and other ground motions on oil and water storage tanks. The results can be extrapolated with reasonable certainty to full-scale tanks.