The paper presents a hydrogen-oxygen gas generator, which could be a key element of a novel scheme of hybrid hydrogen-air energy storage system, which proposes to store energy in both compressed air and hydrogen. At a power generation mode, hydrogen is combusted in oxygen, the produced steam is mixed with air and the gas mixture is used in a conventional gas turbine. The experimental hydrogen-oxygen gas generator has produced gas with temperatures 953-1163 K at pressures 2-4 MPa and has reached the thermal capacity up to 210 kW and thermal efficiency up to 95-99%. Separation of the combustion zone and air injection has helped to reduce NOx, content in the product gas to 11 mg/st.m(3). (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.