A high temperature solid oxide electrolyte fuel cell generator which allows controlled leakage among plural chambers (14, 16, 18) in a sealed housing. It uses a plurality of tubular fuel cells (40), each extending from the combustion product chamber (16) to the generator chamber (14) and being close-ended (44) within the generator chamber. Each oxidant carrying conduit (20) extends through the fuel cell to a point near its closed end to discharge oxidant into the fuel cell. Electrochemical reaction takes place while the oxidant traverses the inside of the fuel cells. Depleted oxidant discharged from the open ends (42) of the cells and hot depleted fuel diffusing through a porous barrier (32) are directly reacted in the combustion product chamber (16) to combust remaining fuel and preheat incoming reactants.