This study uses life cycle assessment to evaluate the relative costs and impacts (e.g. global warming potential) of various waste conversion systems. Eight different technologies are evaluated in Singapore: pyrolysis gasification of Municipal Solid Waste (MSW); pyrolysis of MSW; thermal cracking gasification of granulated MSW; combined pyrolysis, gasification and oxidation of MSW; steam gasification of wood; circulating fluidized bed (CFB) gasification of organic wastes; gasification of RDF; and the gasification of tyres. Results demonstrate that the highest impacts are associated with thermal cracking gasification of granulated MSW and the gasification of RDF; and lowest impact are from the steam gasification of wood and the pyrolysis gasification of MSW. The lowest costs are associated with the CFB gasification of organic waste and the combined pyrolysis, gasification and oxidation of MSW, and high costs are associated with the thermal cracking gasification of granulated MSW and the gasification of tires.