Trim control of a partial oxidation gas generator for the production of synthesis gas, reducing gas, or fuel gas is effected by two improved control schemes which are automatically operated separately or in sequence. The control systems include sensors sensing the flow rate of the feedstreams and analyzers which provide signals corresponding to the wt. % carbon in the effluent gas quench cooling and scrubbing water for use in controlling the particulate carbon in the effluent gas stream, and/or signals corresponding to the mole fraction of CH.sub.4 (dry basis) in the cooled and cleaned effluent gas stream for use in controlling the temperature in the reaction zone. The signals from the sensors and analyzers are provided to the system control unit which computes values that represent the relative difference between the actual and desired carbon-make and/or the actual temperature in the reaction zone, and the relative difference between the actual and desired temperature in the reaction zone. The actual temperature is determined as a function of the methane concentration. These values are automatically compared with set point values and when adjustments are necessary, signals from the system control unit are provided to a flow rate regulating means which adjusts the flow rate of the free-oxygen containing gas by a small determined amount for control of the particulate carbon and/or to a flow rate regulating means which adjusts the flow rate of the temperature moderator by a small determined amount for control of the temperature in the reaction zone.