Vitiated combustion processes offer the potential to improve the thermodynamic efficiency in hydrocarbon-fueled combustion systems, providing a subsequent decrease in energy-specific CO2 emissions along with a decrease in the emission levels of nitrogen oxides (NOx) and particulate matter. The present work comprises an experimental and modeling study of vitiated ethane oxidation in a high-pressure flow reactor, with pressures of 1-6 bar, O-2 mole fractions of 3.5-7.0%, temperatures of 1075-1100 K and 15-18 mole.% H2O. Time-history measurements of species are used to characterize the overall rate of reaction and track the fuel-carbon through intermediate and product species. A one-dimensional mixing-reacting model that accounts for partial oxidation during reactant mixing is used in conjunction with a detailed kinetic mechanism. Changes in competing pathways due to variations in pressure and O-2 mole fraction give rise to the complex pressure dependence seen in the experiments. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.