Modeling of aftertreatment systems for NO, abatement from fuel combustion is a critical step in catalyst design. Selective catalytic reduction (SCR) is a key component in the overall aftertreatment system. In this paper, we focus on developing a detailed elementary reaction mechanism for hydrocarbon (HC)-based SCR on a silver-impregnated monolith catalyst. Rather than developing a single rate expression based on power-law fitting or Langmuir-Hinshelwood kinetics, a detailed microkinetic modeling approach is utilized to capture the essential physics of this problem. Even though the system is complicated, with more than 10 reductants along with some promoting or inhibiting effects of other species, a hierarchical approach for mechanism development is used to retain the simplicity of the mechanism in terms of computational implementation. The HC-SCR mechanism is shown to capture experimental data for all reductants, in most cases, quantitatively. (C) 2009 Elsevier B.V. All rights reserved.