Optimization of hydrocarbon (HC) oxidation over a diesel oxidation catalyst (DOC) requires consideration of (i) HC gas diffusion into the catalyst layer, (ii) HC gas adsorption and desorption from catalyst sites, and (iii) kinetics of the oxidation reaction. We have already reported a brief modeling study that emphasized understanding HC storage and release from zeolitic sites within the DOC [Banno et al., SAE Tech. Pap. Ser. 2004, 2004-01-1430]. In this study, more-detailed DOC modeling was attempted, using a precise gas diffusion model and experimentally determined reaction parameters. The random pore model was used for gas diffusion calculations, to simulate the bimodal nature of the catalyst structure, which has both macroporosity between catalyst particles and microporosity within the zeolite material. HC adsorption capacity, as a function of temperature and HC concentration, was measured by temperature-programmed desorption (TPD). The rate of HC desorption rate was evaluated by changing the TPD ramping rate. The rate of HC oxidation was measured using a model gas reactor. The conversion efficiency of HC, which was calculated by computer simulation with Star-CD software, reproduced the experimental measurements well, as a function of temperature, thus validating the model. The simulation methodology was used to predict two-dimensional (2D) HC conversion efficiency profiles across radial and axial positions of the monolithic catalyst during HC combustion, and it was also applied to estimate the depth profile of adsorbed HC in the catalyst layer.