This paper presents a study on optimization of a fixed bed tri-reformer reactor (TR). This reactor has been used instead of conventional steam reformer (CSR) and auto thermal reformer (CAR). A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methane conversion, hydrogen production and desired H(2)/CO ratio as a synthesis gas for methanol production. A mathematical heterogeneous model has been used to simulate the reactor. The process performance under steady state conditions was analyzed with respect to key operational parameters (inlet temperature, O(2)/CH(4), CO(2)/CH(4) and steam/CH(4) ratios). The influence of these parameters on gas temperature, methane conversion, hydrogen production and H(2)/CO ratio was investigated. Model validation was carried out by comparison of the reforming model results with industrial data of CSR. Differential evolution (DE) method was applied as a powerful method for optimization. Optimum feed temperature and reactant ratios (CH(4)/CO(2)/H(2)O/O(2)) are 1100 K and 1/1.3/2.46/0.47 respectively. The optimized TR has enhanced methane conversion by 3.8% relative to industrial reformers in a single reactor. Methane conversion, hydrogen yield and H(2)/CO ratio in optimized TR are 97.9%, 1.84 and 1.7 respectively. The optimization results of tri-reformer were compared with the corresponding predictions from process simulation software operated at the same feed conditions. (C) 2011 Elsevier Ltd. All rights reserved.