Using a hydrogen/oxygen steam generator it is possible to carry out many steam mixing re-heatings without increasing the complexity of a traditional steam power-plant: steam is not required to re-enter the boiler for each re-heating. An isothermal expansion could thus be approached by means of several adiabatic expansions and several steam mixing re-heatings. A theoretical investigation showed that an isothermal expansion could achieve high efficiency (up to 70% of HHV) when the waste heat at the turbine outlet is recovered for pre-heating water, hydrogen and oxygen. In a real plant the number of re-heatings that can be carried out, although high, is limited and we can therefore expect an efficiency drop which varies as a function of the number of re-hearings, the re-heating temperature and the maximum pressure. In order to evaluate real cycle performance, a numerical code. specifically created, was implemented. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.