Syngas (a.k.a producer gas) is normally made from atmospheric oxygen, and is a conversion process of the stored fuel in biomass through pyrolysis to produce tar

Syngas (a.k.a producer gas) is normally made from atmospheric oxygen, and is a conversion process of the stored fuel in biomass through pyrolysis to produce tar gas, which is then reduced by the hot charcoal left over. You are essentially producing fuel from garbage and is worthwhile on it's own. By using pure oxygen you can produce a more pure gaseous fuel, as the final product isn't diluted by the mostly inert nitrogen that is in air.