Promotion of rhombohedral SmOF by SrF ₂ or BaF ₂ led to significant gain in ethane conversion but little change in ethene selectivity in the oxidative dehydrogenation of ethane. At 893 K, C ₂ H ₆ conversion and C ₂ H ₄ selectivity over SmOF were, respectively, 38.8 and 71.2%. With 10% SrF ₂ /SmOF and 20% BaF ₂ /SmOF catalysts, C ₂ H ₆ conversion became 69.7 and 68.4%, respectively, while C ₂ H ₄ selectivity was 67.7%. X-Ray diffraction (XRD) studies revealed a small amount of cubic SrF ₂ but no crystal phase of BaF ₂ in the promoted catalysts. The SrF ₂ lattice contracted slightly and the SmOF lattices expanded slightly. We believe that such deformities resulted from ionic exchange/substitution occurring between/within the SrF ₂ and SmOF phases with creation of active centres. The Raman and O ₂ temperature programmed desorption (TPD) results, indicated that, above 973 K, dioxygen species on SmOF were converted completely to mono-oxygen species. With the promoted catalysts, such conversion was complete at around 573 K. Because Sm ³⁺ is paramagnetic and owing to the effect of spin–spin interaction, we could not obtain any EPR signals of O ₂ ^- or O ^- over SmOF. Over the promoted catalysts, however, EPR signals corresponding to O ₂ ^- and O ^- located in the proximity of non-paramagnetic Sr ²⁺ and Ba ²⁺ ions were observed. The conversion of O ₂ ^- to O ^- was confirmed and monitored by EPR spectroscopy. We conclude that the deformities generated in the promoted catalysts have facilitated the conversion of dioxygen species to O ^- species at lower temperature, resulting in better catalytic performance.