Single-phase perovskite-like oxides NdSrCu1-xCoxO4-delta and Sm1.8Ce0.2Cu1-xCoxO4+delta (x = 0, 0.2, and 0.4) were prepared using the citric acid complexing method coupled with ultrasonic treatment. We characterized the materials by a number of analytical techniques. It was found that the NdSrCu1-xCoxO4-delta and Sm1.8Ce0.2Cu1-xCoxO4+delta catalysts possess T and T crystal structures, respectively. There are Cu3+/Cu2+ ions and oxygen vacancies in the former and Cu2+/Cu+ ions and extra (over-stoichiometric) oxygen in the latter. We examined the catalytic activity of the materials for methane combustion. Methane conversion increased with a rise in the amount of nonstoichiometric oxygen over the two series of catalysts. It is concluded that oxygen nonstoichiometry and Cu3+/Cu2+ or Cu2+/Cu+ redox couples facilitate the oxidation of methane over the NdSrCu1-xCoxO4-delta and Sm1.8Ce0.2Cu1-xCoxO4+delta catalysts. (C) 2008 Elsevier B.V. All rights reserved.