## 3 Research Methodology  
This study reviewed the existing literature on integrating lean and green principles in the oil and gas industry, specifically emphasizing achieving sustainability. While substantial research has been conducted on applying Lean Six Sigma to enhance operational efficiency within the petroleum sector, there is a notable gap in studies examining the environmental benefits of these practices in the context of sustainability. Consequently, the role of lean and \begin{table}
\begin{tabular}{l l} \hline \hline
**Model** & **Benefits** \\ \hline \multirow{2}{*}{Gemba–Kaizen model [76]} & Reduce resource consumption and improve environmental performance. \\ \hline \multirow{2}{*}{Circular economy model [88]} & Minimizes waste by reducing, reusing, and recycling. \\ \hline \multirow{2}{*}{Sustainable energy management system [89]} & Helps industries identify inefficiencies and implement corrective measures promptly. \\ \hline \multirow{2}{*}{Lean–green decision model [90]} & Effective economic and environmental indicators. \\ \hline \multirow{2}{*}{Self-assessment model [46]} & Assessment of green–lean implementation readiness. \\ \end{tabular}
\end{table} 
Table 4: Lean–green implementation models and their benefits applicable to the SSA Petroleum industry. green principles in promoting environmental sustainability whilst improving operational efficiency within the petroleum industry remains underexplored. An extensive literature review is essential to illuminate the potential of lean-green integration in addressing these environmental challenges. Ref. [97] highlighted that a thorough literature review is crucial for synthesizing current research findings with recent evidence, identifying gaps in knowledge, and guiding future investigations. The methodology used in this review involved the following steps:  
Research questions: This review was guided by two research questions:  
RQ1:What are the lean and green tools/techniques suitable to incorporate sustainability? RQ2:What are the practical strategic solutions to the sustainability challenges In the SSA Petroleum Industry? Time frame: The time frame chosen for this research was 1990 to 2024. The year 1990 was chosen as the starting year since the concept of lean manufacturing was further developed in that year, as can be evidenced in \"The Machine that Changed the World\" [98]. Although the sudden interest in lean and green themes started in 2005 [10; 99], this study returned to 1990 because of the lean concept. Search Engine: Electronic databases were provided by key publishers like Emerald, MDPI, Science Direct (Elsevier), Taylor and Francis, IEEE, Google Scholar, Springer, and key papers from International conferences. Onepetro was used to obtain relevant journals. Search String: Keywords and their combinations were used as the search strategy. These keywords included lean, green, and sustainability, while combinations were performed using the Boolean operators (AND and OR). These included lean and green, lean-green and sustainability, and lean and green in the petroleum industry. The search result was restricted to the English language. Analysis and Synthesis: Several methods can be used in synthesizing qualitative research. This study used the descriptive analysis method to provide a comprehensive overview of existing research on lean and green integration in the petroleum industry. The descriptive method was chosen because it provides a detailed description and understanding of data and answers questions of what, how, where, and why. Microsoft Excel was used to process the data obtained, and 116 articles that matched the study criteria were selected. In addition, Table 5 highlights the methods utilized as revised from the works [10; 42].