This research project investigated the thermochemical behaviour of biomass (cypress wood chips and macadamia nut shells), coal (Australian bituminous coal) and their blends during pyrolysis and combustion using thermogravimetric analysis (TGA) as well as studied the syngas production from gasification of the fuels and their blends at blending ratios (biomass:coal) of 95:5, 90:10, 85:15 and 80:20 on a laboratory scale downdraft gasifier. The key aims of the research were to study the influence of the blending ratios on the performances of the thermochemical processes and to develop a mathematical model that can be used for predicting the results of the co-gasification technology. The results from the proximate and ultimate analyses found that cypress wood chips and macadamia nut shells had relatively similar approximate composition and absolute elemental composition. However, major differences between these two types of biomass and the Australian bituminous coal were observed in several properties including volatile matter, fixed carbon, carbon content and oxygen content.