Here we show that the high-temperature phase stability of the highly potential oxygen-storage material YBaCo4O7+delta is substantially enhanced by replacing part of cobalt by gallium. Our systematic investigation of the YBa(Co1-xGax)(4)O7+delta system reveals that with increasing Ga-substitution level x the temperature where the phase starts to decompose under oxygen-containing atmospheres gradually increases such that for x >= 0.20 no indication of phase decomposition is seen upon heating in 1 atm O-2 up to 1000 degrees C. At the same time, the low-temperature oxygen-storage capability of the phase is somewhat affected by the Ga-for-Co substitution. With increasing x. the oxygen absorption rate gets slower but the amount of excess oxygen tolerated by the structure is little affected such that e.g. under 100 atm 02 pressure the x=0.20 sample could be loaded with excess oxygen up to delta approximate to: 1.2. We discuss the Ga-substitution effects in the present system comparing to those previously observed in the YBa(Co,Al)(4)O7+delta system. (C) 2011 Elsevier B.V. All rights reserved.