This study was carried out to understand the decomposition behaviour of a range of biofuel and waste feedstock during gasification in a downdraft gasifier. A laboratory scale large sample thermogravimetric analyser (LSTA) is used which allows the data on bum-out characteristics of different fuel particles to be measured under agitated conditions. The conditions chosen simulate the combustion behaviour in a gasifier for a range of biofuels and wastes, namely hazelnut, pistachio, and peanut shells, wood chips and sewage sludge pellets. From this data the activation energy is calculated for a heating rate of 20 °C/min. It was found that, as the weight loss increases, the activation energy decreases. In addition the influence of a range of gasification air/N2 levels on constituents of the gas released during hazelnut shell decomposition was observed. It was found that the composition of the product gases consisted of CH4, H2, CO, CO2, C2H4, C2H6. This was analyzed as function of time for hazelnut shells showing that the primary products are H2, CO, CH4 and CO2 .