Tanks are indispensable assets in petroleum refineries and petrochemical complexes, serving as storage vessels for petroleum substances across diverse production stages. The performance of the foundation system plays a critical role in ensuring the efficient function of these tanks. The correct choice of the foundation system and its design are crucial, often relying on thorough soil investigation data. However, inadequate coverage of soil investigation data and high spatial variability of the subsoil can lead to unsatisfactory performance of the foundation system, thereby jeopardizing tank performance.” This study focuses on assessing the performance of a large-diameter floating roof tank, measuring 92 m in diameter and 20 m in height, which rests on improved ground using stone columns. The tank exhibited excessive settlements during hydro-testing, with the maximum total settlement observed was 238 mm, surpassing the permissible limit of 150 mm. Additionally, differential settlements at specific locations exceeded the acceptable limit of 1 in 500. The confirmatory soil investigation during root cause analysis revealed the presence of organic soil patches. The design was re-evaluated considering the revised soil parameters, and a comprehensive performance analysis of the tank was conducted, resulting in the tank's approval for utilization at 100% capacity. Moreover, remedial measures were proposed to address uneven levels at the tank periphery and prevent settlements in the future. This paper emphasizes the importance of location-specific soil investigation data with adequate quantity and quality to eliminate uncertainties arising from data scarcity and inaccuracies during investigations. Critical parameters for tank foundation system selection, detailed performance analysis, and remedial measures for distressed foundations are presented. By addressing these crucial factors, the study enhances the understanding of tank foundation systems, ultimately improving the overall performance and reliability of tanks in petroleum refineries and petrochemical complexes.