The work presents a study on effect of vapor-liquid equilibrium phase behavior on enhanced oil recovery by in situ combustion method. The physical model is compositional in nature and takes into account the advective-reactive mass conservation together with conductive and convective transport of heat through a porous oil reservoir. Peng-Robinson equation of state (PR EoS) approach is implemented in estimating the equilibrium compositions of crude oil components. From the numerical results, the phase behavior of oil is found to have an appreciable effect on reaction rates. The present numerical shows that the composition independent models overestimate a cumulative oil recovery of about 18% of original oil in place than PR EoS approach. Copyright © 2015 Taylor & Francis Group, LLC.