Since 2001, in order to enhance ethanol's cost competitiveness with gasoline, the Thai government has approved the exemption of excise tax imposed on ethanol, controlling the retail price of gasohol (a mixture of ethanol and gasoline at a ratio of 1:9) to be less than that of octane 95 gasoline, within a range not exceeding 1.5 baht a litre. The policy to promote ethanol for transport is being supported by its positive effects on energy security and climate change mitigation. An analysis of energy, greenhouse gas (GHG) balances and GHG abatement cost was done to evaluate fuel ethanol produced from cassava in Thailand. Positive energy balance of 22.4MJ/L and net avoided GHG emission of 1.6 kg CO2 eq./L found for cassava-based ethanol (CE) proved that it would be a good substitute for gasoline, effective in fossil energy saving and GHG reduction. With a GHG abatement cost of US$99 per tonne Of CO2, CE is rather less cost effective than the many other climate strategies relevant to Thailand in the short term. Opportunities for improvements are discussed to make CE a reasonable option for national climate policy. (C) 2007 Elsevier Ltd. All rights reserved.