The Baram Delta Operations (BDO), located offshore Sarawak Malaysia, consists of 9 fields with an estimated STOIIP of about 4 BSTB. 6 of the major fields in BDO have been on production for more than 30 years. Average recovery factor to date is about 30%. EOR has been planned as an effort to boost the production as well as prolong the life of the field. A preliminary EOR screening study shows that water-alternating-gas (WAG) is the most amenable EOR process for BDO. A PETRONAS and Shell joint study team was tasked to further extend the screening study conducted in 2005 by developing an EOR Big Picture for BDO. The objective of the study was to quantify the EOR potential in BDO and to develop a holistic areal implementation plan to mature the EOR potential. Scenarios evaluated involved a combination of three gas processes; immiscible hydrocarbon (HC) WAG as well as immiscible and miscible carbon dioxide (CO2) WAG. All reservoirs in BDO were first screened and ranked. Eligible reservoirs were then characterized into a few groups according to fluid, rock type as well as aquifer and gas cap size. Optimized EOR performance was evaluated using full field models as well as smaller scale, detailed prototype models of a few selected reservoirs. The prototype models were developed using field analogue data which were representative of a particular reservoir group. The performance prediction of the remaining reservoirs not modeled was STOIIP scaling of representative dimensionless curves. The HC WAG reservoirs were all immiscible while the potential CO2 WAG was a combination of miscible and immiscible cases. The subsurface EOR evaluation also included an estimation of infill and water flood potential, associated well count, well cost as well as the net gas import required and the total gas handling required. This paper presents the details of the systematic approach used to assess the subsurface EOR potential in the BDO fields.