In-situ combustion (ISC) is an enhanced oil recovery method that involves coupled mass transport, fluid phase equilibria, and chemical reactions. Because of its complexity, a full understanding of ISC process phenomena and their modeling remains an open research topic. Ramped temperature oxidation (RTO) of crude oil is one of the methods to obtain the kinetics of oxidation. This paper provides a new method to interpret such. RTO experiments and then gives an improved physical understanding compared with classical analytical methods. The reactor model is based on a compositional and full equation of state formulation. The numerical model is applied to a synthetic test case. Although generally not taken into account, this work shows that spatial transport effects are present despite the plug flow design of typical RTO reactors. Moreover, coupling between thermodynamics and chemistry is important even for extra-heavy oil that in a first approximation could be seen as totally nonvolatile.