This dissertation develops a systematic targeting method based on the C-H-O ternary diagram for the conceptual design of gasification-based biorefineries. The approach is applied using dimethyl ether (DME) as case study. A stoichiometric equilibrium model is presented for calculation of the C-H-O chemical equilibria to evaluate and predict equilibrium syngas composition, operating temperature, type and amount of oxidant required in biomass gasification. Overall atomic species balances are developed and process targets are plotted on the C-H-O ternary diagram. Sustainability metrics are incorporated to provide useful insights into the efficiency of biorefinery process targets. It was found that syngas at 1200 and 1500 K is predominantly H2 and CO. Moreover, DME biorefineries have two main process targets, based on the indirect and direct synthesis routes. Gasification at 1200 K and 1 atm. using H2O/CO2 = 2.642 (w/w) and H2O/CH4 = 1.645 (w/w) achieved syngas composition targets for the direct and indirect methods respectively. Comparatively, the integrated biorefinery based on indirect route was more efficient, producing 1.903 ton of DME per ton of biomass feedstock. The process is 100% carbon-efficient and recycles 1.025 tons of H2O. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)