An oil storage tank that suffered damage during the 1979 Imperial Valley earthquake is studied using a laboratory model. The tank is unanchored and includes a floating roof. The tank is subjected to a single horizontal axis base excitation. Buckling is studied under both harmonic and simulated earthquake base motion. The model buckling results are in reasonable agreement with the field observations. It was also found that the floating roof has no effect on the buckling behavior. Comparison with the API design provisions shows that the empirical model used as the basis of the code for both tip-over and buckling have little resemblance to the actual tank behavior.