Due to the sudden nature of hull girder collapse caused by extreme loadings, the ultimate strength of ships, i.e., ultimate capacity, has to be evaluated. Ultimate strength analysis procedures have already been provided within the rules of the classification societies for sea-going ships. However, rules for inland vessels are not fully addressing the issue. In addition, literature data on the ultimate strength of inland vessels are almost negligible, which is alarming, considering the frequency of grounding and overloading events in inland navigation. Moreover, inland vessels' structural elements are prone to buckling due to their slender plates. In order to evaluate ultimate strength, an inland waterway (IW) barge is chosen for progressive collapse analysis (PCA) employment. PCA has demonstrated that the buckling collapse of structural elements vastly governs a vessel's ultimate capacity. Results show the extent of the safety zone between the actual loss of the ultimate capacity and the linear-elastic behavior of the structure.