The selective detection of hydrocarbons using portable microsensors remains a fundamental challenge in materials and microsystem development. This work describes the functioning of a proposed thermoelectric catalytic microsensor using a metal oxide catalyst and a selective partial oxidation reaction for ethanol detection in complex hydrocarbon mixtures containing hundreds of hydrocarbons present in gasoline fuel. In the case where the competing hydrocarbons are nonreactive, 100% selectivity toward ethanol would be obtained and quantification is straightforward-this case is simulated using ethanol in an inert atmosphere. As an example of detection and quantification in the presence of other reactants, a two step detection sequence is presented for the identification of ethanol concentrations in a hydrocarbon mixture containing methanol. Two-dimensional COMSOL simulations are performed, using known kinetic parameters for ethanol and methanol partial oxidation to acetaldehyde and formaldehyde, respectively, over the chosen iron molybdate catalyst at 353 K, to characterize temperature and concentration profiles within the microelectric thermal sensor/catalytic microreactor, which in turn can be used as a database for a genetic search algorithm used in a real device under unknown environments. Additionally, the knowledge of expected temperature profiles allows one to optimize design parameters for the device to maximize sensor sensitivity and performance for ethanol/methanol verification in complex mixtures.