An uncommon oxygen absorption/desorption behavior for cobalt oxide YBaCo4O7+d was found[Karppinen et al. Chem Mater 18 2006 490]. Y114 absorbs and desorbs oxygen up to d = 1.5 in anarrow temperature range <400 °C. The process is highly reversible, being controlled by bothtemperature and O2 partial pressure. Such a large low-temperature oxygen-content tunability is ofgreat promise in regard to applications related to, e.g., oxygen storage. Huq et al. [JSSC 179 20061136] showed that as-synthezised Y114 is biphasic and suggested that oxygen absorption takesplace in one of the phases. By means of HT-NPD in O2 atmosphere we shall i) monitor thecrystallographic changes in Y114 during the capture and release of O in the material, ii) solve thestructure of the O rich form, and consequently iii) solve and explain the oxygen absorption/desorptionmechanism in this interesting new material.