Enhanced Oil Recovery (EOR) is one of the focus area for Malaysia's offshore oilfield (Yassin, A. A. M.: 1988, Hamdan M. K. et al: 2005 and Samsudin Y. et al: 2005) to unlock remaining oil inside the reservoir for recovery beyond waterflood, 30% (PE Hanbook, 1992), and as of January 2005, the average oil RF for Malaysia producing oil field is standing at 33% derived from 17.0 Bstb STOIIP, Samsudin, Y. et al (2005). The Malaysia's EOR processes studied were involved chemical, gas flooding and microbial which it has considered having the most practical aspects based on the characteristics of the oil; for light oils, facilities readiness and bundant of produced water and seawater. The most optimum EOR process is proposed for water-alternating-gas (WAG), Wan-Mohamad W.N. et al (2005) and Selamat S. B. et al (2008) and Abu Bakar M. et al (2011). This paper, is to provide an alternative solution for the WAG process by introducing chemicals into both water and gas slugs to further enhance displacement efficiencies. The study requirement was based on, firstly is to further enchance WAG process, secondly, WAG investment protection and thirdly, in overcoming the existing process of foam assisted WAG (FAWAG) limitations such as foam callapse and short propagation distances, Blaker T. et al (1999), Skauge A. et al (2002) and Aarra M.G. et al (2002) from Snorre field pilot experience. This process is called as an in-situ-FAWAG or icFAWAG and discussion focus is on 1D coreflood modelling, which the production matching quality is guided material balance under hybrid condition between alkali, acid and foam flooding. The production is derived from 1-meter coreflood or displacemnet result and meanwhile, the formulation (icFAWAG) properties are obtained from fluid-fluid result, tested in one of Malaysia oil producing field, which the field is undergoing WAG development. The physics and chemistry reactions was modeled using 2016 CMG STAR simulator. Amongst the key finding are, (1) the alternative process of foam flooding, icFAWAG formulation is capable to achieve higher oil recovery, 82.5% than WAG and FAWAG and this contributed by sweep efficiencies improvement, stable foam front, additional >5% RF, (2) reasonable material balance result was achieved based on average historical matching quality index (HMQI) result for oil, water, gas production and pressure, is at 0.5, and (3) Achieved fit-for-purpose icFAWAG modelling workflow and it consisted of 5 steps and the detail sub-workflows were established up-to level 3/4 descriptors. This workflow can be considered a hybrid process to cater 3 chemical reaction modelling; FAWAG (surfactant-gas), straight chemical flooding (A-SP) and acid.