Enhanced Oil Recovery (EOR) techniques are crucial for maximizing hydrocarbon extraction from mature oil fields. Among these techniques, Water-Alternating Gas Injection (WAG) stands out as a particularly promising strategy for addressing challenges related to superseding and under-riding phenomena, especially in viscous mature oil fields. This paper explores the effectiveness of WAG injection as an EOR method, with a focus on optimizing recovery efficiency using the Cmost optimization tool (CMG). Field-A, located in northeastern Oman, exemplifies the geological complexity typical of such fields, with its unique challenges including fractures and diverse lithology. Gas injection in Field A is particularly challenging due to these fractures and high permeability streaks, which lead to a disproportionate amount of gas relative to oil. Despite these challenges, Field-A remains integral to Oman's hydrocarbon portfolio and has undergone various development strategies, from solution drive to water flood projects. Optimizing injection techniques, especially WAG, is essential to overcoming these challenges and maximizing recovery rates. Optimizing multi-objective function using particle swarm optimization has yielded in maximizing cumulative oil production and minimizing cumulative gas over oil ratio and minimizing cumulative water production. The optimizations were executed for bi-objective and tri-objective variables. Bi-objective optimization has resulted in a pareto solution with maximum cumulative oil rate of 133 X1000 Mm3 with cumulative gas over oil ratio of 139 mm3/mm3. In other side, tri-objective variables were conflicted and bounded by third variable which is minimizing water production. However, the result of tri-objective has shown same to bi-objective optimization. In conclusion, this study investigates optimizing oil production through bi-objective and tri-objective approaches. The bi-objective optimization focuses on maximizing cumulative oil production and minimizing the gas-oil ratio, significantly improving oil production and efficiency compared to the base case. The tri-objective optimization, which includes minimizing cumulative water production, results in more dispersed solutions, offering a broader range of operational options. Adjustments in gas and water injection rates are crucial in achieving these optimized outcomes. The study demonstrates substantial improvements in reservoir performance through strategic optimization, providing valuable insights for enhanced oil recovery strategies.