The major goal of the research is to develop a stable, effective and controllable biomass gasification process and produce an environmentally friendly energy resource – fuel gas, which could be used in internal combustion engines for energy production. A new type of a pilot scale stratified downdraft gasifier has been developed with the aim to provide a controllable process of gasification of wood and wheat straw pellets and their mixtures by varying the air supply rate and additional heat energy supply with propane flame flow into the gasifier. The composition of the produced fuel gas (CO and H2) as well as the produced amounts of ash, chars and tars are estimated and analyzed taking into account the effect of operation condition variations on the gasification process.