Abstract This paper presents an integrated evaluation of enhanced oil recovery (EOR) in a complex carbonate reservoir using the miscible water- alternating-gas (WAG) method, focusing on the interplay between analytical models, compositional simulation, and equation of state (EoS) upscaling. The reservoir under study is a heterogeneous pre-salt carbonate containing low-viscosity volatile oil with a high gasoil ratio (GOR) and significant CO2 content in the flashed gas. The primary objectives are