Continuous NOs reduction by octane under lean conditions over a highly active Ag/alumina catalyst was studied. Experimental data, observed at steady-state conditions, was used to produce a phenomenological kinetic model to determine the rate orders in NO, hydrocarbons and O-2. The results showed that the reaction order in NO was equal to zero in the temperature range of 300-550 degrees C. However, at the same time reaction orders in octane exceeded unity, and were dependent on the NO concentration. Mechanistic model was developed, which takes into account kinetic regularities. (c) 2004 Elsevier B.V. All rights reserved.