The influence of the reaction medium (steam) and the amount supplied to the reactor (~200, 400, or 600 mL) on the yield of the basic gas components (CO, CO2, H2, and CH4) in microwave pyrolysis of sawdust is investigated. The dependence of the mean and maximum gas concentrations on the volume of steam supplied to the chamber of the microwave generator is determined. Trends in the gas concentrations over time are identified. The onset and duration of gas emission are established with variation in the volume of steam supplied to the reactor. The optimal supply of reaction medium to the chamber is determined, such that biomass pyrolysis is intensified and the gas yield is a maximum. If excessive steam is supplied to the chamber, the yield and composition of the producer gas become worse.