<p>In this review, the optimal conditions of transesterification of waste cooking oil to produce biodiesel are examined, including methanol:oil ratio, catalyst concentration, reaction temperature, and reaction time. Within the scope of this review, the key process parameters include feedstock type, catalyst selection, reaction conditions, and biodiesel yield across different sources. This review consolidates the recent findings (inclusive of data for 2025) reported in one place, highlighting common trends, discrepancies, and research gaps. For this review, a critical analysis was conducted to assess the scientific and engineering challenges, particularly in catalyst efficiency, pretreatment methods, and economic feasibility. The key findings are identified to be a lack of economic and environmental data that could assist in formulating potential largescale waste cooking oil transesterification systems for biodiesel production. Studies report varying conditions, hindering the establishment of a standardized process for maximizing biodiesel production efficiency. Factors such as feedstock availability, catalyst recyclability, and energy consumption require further study to determine the long-term feasibility of biodiesel from waste cooking oil as a sustainable alternative to fossil fuels. Addressing these issues is crucial for optimizing transesterification of waste cooking oil for biodiesel production at an industrial scale. The findings highlight the need for optimized transesterification parameters, cost-effective catalysts, and scalable pretreatment methods to enhance biodiesel yield, reduce production costs, and improve economic and environmental sustainability for industrial applications.</p> Graphic abstract <p></p>