The oxidative dehydrogenation of ethane in the presence and absence of tetrachloromethane (TCM) has been investigated over MgSO4 at reaction temperatures between 723 and 998 K. Although the conversion of ethane over MgSO4 was increased on addition of TCM to the feedstream, the ethylene selectivity was not influenced except at 723 K. The results of XRD and XPS measurements suggest that MgCl2 is formed on the surface of the the catalyst from the vapor phase TCM and may be responsible for the effects observed in the presence of TCM. At reaction temperatures greater than 898 K, higher conversion of ethane can be attributed to the formation of MgO from the decomposition of MgSO4.