Biomass conversion processes producing oil, ethanol, methanol and hydrogen were evaluated in terms of energy payback time (EPT), CO2 emissions and product cost. The annual production rate of each process evaluated was 1.07 x 10(7) GJ. All of these systems had EPT in the range of 5-75 days, and the CO2 emissions ranged from 11 to 142 kg-C/TOE, which is around 1-20% of typical emissions from power generation by fossil fuels. We therefore showed that biomass energy plantations and conversion systems are an effective source of renewable energy, and can help reduce the global CO2 emission budget. Product costs are estimated to range from 21,100 to 35,100 Japanese yen/TOE, and are only 1.8-3 times the cost of current oil-burning power generation systems. (C) 2001 Elsevier Science Ltd. All rights reserved.