In an effort to eliminate problems previously experienced in fabrication and installation of large steel structures, emphasis for the Ninian field southern platform was placed on designing for those factors as well as for functional and long-term loadings. This paper describes design and innovative features of the structure. Introduction Chevron's Ninian field southern platform is noteworthy for its rapid planning, design, fabrication, and extremely successful installation, all of which justified the conceptual philosophy adopted early in the design stage. The aim was to build on past experience and to provide simplicity and refinement within the limits of available technology, consistent with a summer 1977 installation of a platform capable of supporting the heaviest deck load yet proposed for a piled steel structure. These goals, together with severe functional and environmental criteria, resulted in a number of interesting features.This paper describes the process leading to the selection of a self-floating steel tower and outlines the manner in which considerations of fabrication, transportation, and installation influenced the configuration of structure and piles. Selection of Platform Type, Factors Influencing Configuration It was believed that the success of the proposed program would rely as much on designing for fabrication and installation requirements as on structural analysis and design. In the overall development cost, the effect of saving structural steel weight by virtue of exhaustive analytical work is insignificant; on the other hand, time spent on designing for fabrication and installation can result in significant cost savings. Description of Tower The Ninian field southern platform is a four-leg, piled, steel-tower structure supporting modular production and drilling facilities (Fig. 1). It is a self-floating unit with an integral ballasting system designed for remote-controlled operation.The deck comprises two levels of modules, 65 × 68 m in plan, providing three main levels, with a nominal production capacity of providing three main levels, with a nominal production capacity of 150,000 BOPD. Maximum anticipated deck load is 26 000 t, including two drill rigs. Slots are provided for 42 conductors.Typical dimensions are 75 × 75 m center to center of the legs at the mudline, tapering to 55 × 55 m at the top of the module support skid beams. Overall height from mudline to skid beams is 168.5 m.The tower is supported by 32 skirt piles, 1825 mm OD with walls 63 mm thick, arranged in clusters of eight at each leg in a 12.2-m diameter circular pattern.Storage is provided in the upper parts of the 9.2-m diameter flotation legs for 20,000 bbl of diesel fuel and 10,000 bbl of drilling water. JPT P. 1366