We have examined species and temperature profiles for oxidative dehydrogenation of ethane within and after Pt and Pt-Sn catalysts both with and without hydrogen addition. We investigated the roles of oxidative and non-oxidative chemistry as well as the roles of heterogeneous and homogeneous chemistry. For Pt, considerable ethane was consumed after the 10 mm catalyst and significant oxygen breakthrough occurred. Without hydrogen addition, approximately half of the ethane chemistry occurred after the Pt catalyst, and with hydrogen addition, almost all of the ethane chemistry occurred after the Pt catalyst. For Pt-Sn, most of the ethane and almost all of the oxygen were consumed within the 10 mm catalyst. The front face of the Pt-Sn catalyst was 150-200degreesC hotter than Pt, and the back face of the Pt-Sn catalyst was 100degreesC hotter than Pt. By varying the length of the catalyst from I to 10 mm, we observed no appreciable change in the reactant conversions or effluent product distributions versus length. We conclude that the catalyst consumes ethane or hydrogen in heterogeneous combustion reactions. The heat from these reactions then drives the endothermic dehydrogenation of ethane to ethylene, with homogeneous chemistry playing a significant role in ethylene production. Since the addition of tin is unlikely to improve the activity of the Pt catalyst, we suggest that the primary role of tin is to prevent ethane decomposition to carbon on the catalyst surface, which would ultimately lead to CO and CO2. This implies that the Pt-Sn catalyst would have more platinum sites free for O-2 adsorption, which in turn leads to more hydrogen oxidation on the Pt-Sn surface, a higher catalyst temperature, and less CO and CO2 production.