Mixture effects are observed when ethanol is oxidized in mixture with benzene or elhenylbenzene (styrcne). Very lean mixtures (<2000ppmV) were tested over a commercial monolithic catalyst. In the mass transfer controlled regime higher conversions are obtained for ethanol in mixture with aromatic, due to the increased adiabatic temperature rise; but the ignition temperature increased. The hydrocarbon reaction rate is slightly affected, while ethanol oxidation (either complete or partial) is strongly inhibited, especially by elhenylbenzene. The selectivity of the reaction is modified, but the significant reduction in aldehyde emissions all over the temperature range is mainly due to the strong inhibition at low temperature and to the increased ignition temperature