We present a three-dimensional (3-D) steam-methane-reforming (SMR) model consisting of a steam-reforming (SR) reactor, water gas shift reactor, preferential oxidation reactor, catalytic burner, heat exchangers, and balance of plant components. The mass and energy balance equations are derived considering the kinetic expressions of various SMR reactions and implemented in the commercial computational fluid dynamics software program Fluent by employing user-defined functions. The 3-D SMR model is then applied to a 10-kW SR reformer geometry and simulated for comparison with in-house experimental data. The simulation results and the experimental data show good agreement, and the model accurately captures the experimental exhaust gas compositions and the reactor outlet temperatures. The proposed 3-D simulation tool for predicting various transport and chemical processes is highly desirable from the viewpoint of design and optimization of full-scale SMR-based fuel processors.