South Africa’s ageing petroleum refineries face operational inefficiencies, high costs, and increasing pressure to meet stringent environmental regulations. This study investigates the performance gaps between local refineries and leading international counterparts, aiming to identify critical success factors (CSFs) for transformation. A mixed-methods approach was employed, combining quantitative survey analysis (n = 79) with qualitative thematic coding of expert insights. Findings reveal that South African refineries adopt compliance-driven, reactive strategies with limited investment in automation, advanced process control, and workforce development. Key improvement areas include technology upgrades, energy efficiency, environmental compliance, and skills enhancement. The research proposes a practical framework to guide modernisation, emphasising proactive, performance-driven strategies to improve reliability, sustainability, and competitiveness. These insights offer actionable recommendations for decision-makers and investors seeking to transform ageing refineries from the lower standard to global best-practice standards.