Synthesis of methanol is one of the ways of conversion of the greenhouse gas CO2 into an useful chemical. Methanol is synthesized from a feed mixture comprising of primarily CO, H2, and CO2. The objective of the present work is to study the effect of feed composition on synthesis of methanol. First, the conditions under which the kinetic approach and the thermodynamic approach are equivalent are established. The performance characteristics of the reactor under single phase and two phase conditions are then analyzed using the thermodynamic approach. The Gibbs free energy minimization approach is implemented using Aspen Plus for this purpose. The effect of feed composition on the overall conversion of CO + CO2 to methanol and conversion of CO2 is depicted as contour plots for isothermal and adiabatic operations. These can be viewed as performance characteristics of the reactor which aid in selection of suitable feed composition for maximum methanol productivity and CO2 utilization. © 2015 Elsevier Ltd.