The whole integral gas producer system has been designed to be completely self contained, even on remote sites where clean suitable dry wood blocks or coarse chips of correct shape and size, or high density sawdust or agricultural harvest waste briquette fuel can be produced economically, or be supplied at a competitive affordable price from a reliable nearby outside source.

Small pulp wood chips can not be used for tar free gas generation, since the small restricted voids between the pulp chip "particles" prevent sufficient primary air penetration. Wood fuel made from most species of both hard and soft wood with the bark left on, including most of the many economically very important alien wood species growing in Africa and other countries, work well as long as the fuel is dry and of the correct piece shapes and sizes and free of slag forming impurities as specified in the Operator’s Instructions. Dry coarse chips and high density sawdust- and ground nut husk briquettes have also worked well as fuel.

Analysis carried out on char produced from high density grass briquettes indicate that these would also work well as fuel. The maximum moisture content for biomass fuel should, however, not exceed 20% by weight when expressed on wet basis, but it is more economical to use dryer wood fuel. The "critical self flow-through volume weight" of the fuel must not be less than 200 kg/m3 or briquettes with a density of at least 1,200 kg/m3 solid mass and of the correct size and piece shapes should be used for reliable safe, continuous self-flow-through. With most wood species this poses no problem.

If it is planned to use any fuel which has not been tested with the gas producer system, it would be advisable to carry out tests. These tests should include determination of the loose volume weight of the fuel, the ash content, the carbon yield and char softness/hardness properties and if possible also the ash cintering temperature and the CAB (critical air blast) value for the char as well as the char reaction time and reaction temperature.

Reprocessed fuel containing plastics can not be used, since the chlorine produced at the high hearth temperature would very quickly destroy the hearth. Also fuel containing sulphur must not be used.

If old waste wood fuel should contain formaldehyde or melamine glues, ammonia would then be produced and contaminate the gas while damaging the aluminium alloy parts of an engine and also causing air pollution.