Kinetic and isotopic tracer and exchange measurements were used to determine the identity and reversibility of elementary steps involved in ethane oxidative dehydrogenation (ODH) on VOx/Al2O3 and VOx/ZrO2. C2H6-C2D6-O-2 and C2H6-D2O-O-2 react to form alkenes and COx without concurrent formation of C2H6-xDx or C2H4-xDx isotopomers, suggesting that C-H bond cleavage in ethane and ethene is an irreversible and kinetically relevant step in ODH and combustion reactions. Primary ethane ODH reactions show normal kinetic isotopic effects (k(C-H)/k(C-D) = 2.4); similar values were measured for ethane and ethene combustion (1.9 and 2.8, respectively). O-16-O-18(2)-C2H6 reactions on supported (VOx)-O-16 domains led to the initial appearance of O-16 from the lattice in H2O, CO, and CO2, consistent with the involvement of lattice oxygen in C-H bond activation steps. Isotopic contents are similar in H2O, CO, and CO2, suggesting that ODH and combustion reactions use similar lattice oxygen sites. No (OO)-O-16-O-18 isotopomers were detected during reactions of O-16(2)-O-18(2)-C2H6 mixtures, as expected if dissociative O-2 chemisorption steps were irreversible. The alkyl species formed in these steps desorb irreversibly as ethene and the resulting O-H groups recombine to form H2O and reduced V centers in reversible desorption steps. These reduced V centers reoxidize by irreversible dissociative chemisorption of O-2. A pseudo-steady state analysis of these elementary steps together with these reversibility assumptions led to a rate expression that accurately describes the observed inhibition of ODH rates by water and the measured kinetic dependence of ODH rates on C2H6 and O-2 pressures. This kinetic analysis suggests that surface oxygen, OH groups, and oxygen vacancies are the most abundant reactive intermediates during ethane ODH on active VOx domains.