Compression tests were conducted on high-strength single-cell and multiple-cell box sections with plate width-to-thickness (b/t ) ratios ranging from 48 to 96. Local plate buckling occurred at stresses as low as 5 percent of the yield stress, whereas the ultimate compression stress ranged from 38 to 72 percent of the yield stress. These critical stresses were not significantly affected by the length of the specimen, the number of cells, the boundary conditions, or lateral load. Simple empirical design equations based only on b/t gave estimates of the collapse strength within five percent in all cases. Finite-element analyses were able to predict the significant reserve load-carrying capacity and ductility after ultimate load, which was dependent on the length of the specimen as well as the b/t ratio.