The absorption and desorption pressure-composition isotherms in a palladium-tritium system have been experimentally measured at 35, 50, 65 and 75 degrees C using the PVT method for tritium storage up to 3 years. Results show that the storage properties are remarkably well preserved during aging, and only small modifications of P-c isotherms are observed: a decrease of plateau pressures and shifts of alpha single phase regions toward greater stoichiometries. At a temperature in the range 35-75 degrees C, absorption transition enthalpies of aged palladium tritide is 30.1 kJ/mol, desorption transition enthalpies of the unaged is 34.6 kJ/mol and absorption-desorption transition entropy of the aged palladium tritide is less than the unaged. The hysteresis coefficient decreases with the temperature. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.