The Green supply chain management (GSCM) implementation is becoming a widespread concept around the world. It increases the awareness to target environment sustainability while focusing on achieving high-level of performance. This study conducted within Oman's Oil & Gas industries, intends to explore the influence of GSCM adoption on environmental performance, a vital aspect of sustainability. Furthermore, the study investigates how the implementation of internal environmental management effects the adoption of GSCM practices. Using a quantitative method, the study collected data from 131 participants through a questionnaire and analyzed by using Smart PLS. The findings highlight the positive relationship between the implementation of Internal Environmental Management and the adoption of GSCM activities such as green manufacturing, green purchasing, and customer collaboration. Notably, in the context of the oil and gas business, the study finds no significant links between green manufacturing, green purchasing, and environmental performance, while indicating a moderate influence of customers collaboration on environmental performance. This study expands our understanding of the subtle relationships between various GSCM components and sustainability performance metrics, providing significant insights for practitioners facing GSCM implementation issues. Furthermore, it contributes to the knowledge database, laying the groundwork for future research. Aligned with Oman 2040's vision of a green and circular economy, this research emphasizes sustainable practices, such as using natural resources wisely to create high added value while maintaining a balance between environmental, economic, and social needs in accordance with sustainable development principles.