In this study, the process optimization of a tri-reformer reactor is conducted for the synthesis of hydrogen gas from natural gas using multi-objective optimization (MOO) approach. Specifically, four MOO problems are solved using three objective functions, namely maximization of H2, minimization of CO2, and minimization of power loss. It should be noticed that the power loss is an important economic factor due the large pressure drop and flowrates in packed bed reactors. However, it has not been used as an objective function for the optimization based design and/or operation of fixed bed reactor for reforming process to the best of authors’ knowledge. Three of the four MOO problems are 2-objective in nature with all the permutation and combination of the three objectives. The fourth MOO problem is solved considering all the three objectives, simultaneously. For all the MOO problems, feed conditions of O2, H2O, and Temperature are considered as the optimization variables. The results obtained with 3 objective functions are observed to be superior to the ones obtained from 2 objective problems. •Two and three-objective optimization of a fixed-bed reactor using NSGA-II.•Study of tri-reformer reactor for the production syn-gas from natural gas.•Maximization of H2 production and minimization of power loss & CO2 emission.•Optimization variables are feed temperature, steam/methane, and oxygen/methane.