Abstract: The specification discloses an automatic sequencing control system for operating a unit consisting of a pair of oil gas-producing generators in staggered sequence, each generator of which comprises a cooperating pair of reactor shells functioning alternately in a forward direction of product gas flow and in a reverse direction of product gas flow. The control system includes a start-up control, a burner control, a burner fuel ignition control, and an electric power failure control for heat and make periods of operation. An individual reverse flow wash box is provided for each generator and also a waste heat boiler common to both generators, valving for which is under control of sequencing control apparatus.The method of operation of a pair of generators disclosed enables operation within a narrow range of temperatures for long periods of time and without necessity for repair or rebuilding of reactor chambers.