Low emissions and high efficiencies can be realized in combustion systems that operate at high-pressure and low-temperature conditions (high densities). The design of such engines relies on accurate models of the physical processes involved. Under these conditions, the ideal gas model widely used in computational fluid dynamics (CFD) simulations fails to properly capture the relation among pressure, density, and temperature as well as inter-relations among other thermodynamic and transport properties. As such, discrepancies between experimental observations and CFD simulations cannot only be traced to uncertainties from experiments, turbulent, or combustion models. This paper offers a possible solution to the implementation of the real gas equation of state models in combustion simulations. The large number of species in combustion simulations requires effort to provide the relevant real gas properties. A method is suggested for incorporating these properties in simulations based on available transport and thermodynamic data of chemical kinetic models. This attempt also brings out an often-ignored problem in existing chemical kinetic models in the literature, namely, the nonsystematic assignment of transport properties for various species. To clearly demonstrate the need for real gas models in reacting flows, simulations are carried out of a high-pressure n-heptane jet into a quiescent chamber of air based on ideal gas and real gas models. The defects of the ideal gas model are revealed, and the proposed method of property estimation is justified as a convenient solution.