An assessment of net energy and supply potentials was performed to evaluate cassava utilization for fuel ethanol in Thailand. Just recently, the Thai government approved the construction of 12 cassava ethanol plants with the total output of 3.4 million liters per day by the next 2 years (2007 and 2008). The cassava fuel ethanol (CFE) system involves three main segments: cassava cultivation including processing, ethanol conversion, and transportation. All materials, fuels, and human labor inputs to each segment were traced back to the primary energy expense level. Positive Net Energy Value and Net Renewable Energy Value, 8.80 MJ/L and 9.15 MJ/L, respectively, found for the CFE system in Thailand proved that it is energy efficient. Without coproduct energy credits, CFE in Thailand is even more efficient than CFE in China and corn ethanol in the United States. Regarding supply potentials, about 35% of the national cassava production would be used to feed approved CFE factories. A shift of cassava to ethanol fuel rather than its current use for chip/pellet products could be a probable solution.