The praseodymium oxide redox system releases and incorporates oxygen into an inert gas. Reductions of Pr6O11 to Pr5O9 and Pr5O9 to Pr9O16 were analyzed while heating a mixture of air with N-2 at O-2 partial pressures of 2 x 10(2)-6 x 10(3) Pa from 373 to 833 K. Oxidations of Pr9O16 to Pr5O9 and Pr5O9 to Pr6O11 were analyzed while cooling from 873 to 373 K. The enthalpy changes for oxidation reactions (5Pr(9)O(16) + 1/2O(2)--> 9Pr(5)O(9) and 6Pr(5)O(9) + 1/2O(2)--> 5Pr(6)O(11)) were determined to be -128 +/- 26 and -138 +/- 10 kJ, respectively. The oxygen pump with praseodymium oxides incorporated can be operated between air and a gas with P-O2 of 4 x 10(2) Pa by using a temperature-swing method between 403 and 873 K. The minimum P-O2 in diluent N-2 achieved was 0.1 Pa at 403 K.