A method for producing a hydrogen containing gas for use in an internal combustion engine system is provided. The method includes cyclically operating at least two pressure swing reformer reactors such that one is reforming while another is regenerating, thereby producing a continuous stream of hydrogen containing gas. During engine operation exhaust gas is fed to the pressure swing reformer reactor that is undergoing regeneration, thereby supplying at least part of the heat for regeneration. Also, the hydrogen gas produced is used in at least one of (i) the engine; (ii) an engine exhaust treatment device; and (iii) a fuel cell.