Optimize the use of biogas in an engine generator set to produce usable thermal and electrical energy by controlling air fuel ratio and ignition timing. The proportion of electrical and thermal energy was also determined. All experimentation was with a stand-by engine generator set operating on natural gas in laboratory conditions;The first stage of the investigation was to develop a data logging and control system to measure engine parameters and control engine variables. Parameters measured were: mass gas flow rate, mass air flow rate, air fuel ratio, engine coolant inlet and exit temperatures, coolant flow rate, gas temperature, air temperature, engine speed, exhaust temperature and generator power. The variables controlled included: ignition timing, air fuel ratio, coolant exit temperature and electrical power. All parameters and variables (except electrical power) were measured and controlled by a microcomputer and interface system;Secondly, the system was used to determine the relation between ignition timing, air fuel ratio, electrical and thermal energy conversion from natural gas for different electrical loads and constant engine temperature. It was found that the ignition timing had little effect on thermal energy, but for near maximum electrical load, the maximum electrical efficiency was with an ignition advance of 23 degrees BTDC. Optimum air fuel ratio for total energy production (thermal + electrical) was found to be in the range of 17.8 to 19.8;Finally, a simple control system to maintain the air fuel ratio within the optimum range was developed using an automotive exhaust oxygen sensor. A zirconium dioxide sensor and a voltage comparator circuit was used for this purpose.