Floating production, storage, and offloading systems (FPSOs) have been widely used for the development of offshore oil and gas fields because of their many attractive features. They are mostly ship-shaped and either converted from existing tankers or purpose-built. However, FPSOs have their own unique characteristics, including various operational requirements. In addition to that, the expectation of safety and economic aspects of FPSOs require an optimized structure to be designed. This calls for reliable structural assessment methodologies. One of the most important aspects of FPSO structural design and assessment is the hull girder ultimate strength. In this paper, different methodologies of hull girder ultimate strength assessment will be introduced and numerical calculations of hull girder ultimate strength will be presented based on six different FPSO designs. The results will then be analyzed in terms of their differences, and conclusions will be made based upon reliable methodologies for hull girder ultimate strength assessment of FPSOs.