The existing energy-use pattern, based on the prevailing cultivation practices and the optimal energy-demand based on the optimal mechanization strategy for animal operated paddy farms of Assam (India) were assessed. Two categories of paddy farms, i.e. with and without the use of chemical fertilizers were identified. Lower yield (1976 kg/ha) associated with a lower energy-input (5681 MJ/ha) was the characteristic feature of farms not using fertilizer in contrast to the higher yield (3165 kg/ha) and energy input (9290 MJ/ha) of fertilizer-user farms. Human and animal (as also chemical fertilizer for fertilizer-user farms) were the major energy sources under the existing practices contributing to more than 70% of the total energy-input. The optimal demand of energy to achieve a potential paddy yield of 6000 kg/ha was estimated as 11,168 MJ/ha comprising human, animal, diesel, and fertilizers as the major energy sources. Though the overall energy demand increased, the introduction of improved tillage implements could reduce the future optimal demand of animal energy for animal-operated paddy farms in Assam. (C) 2004 Elsevier Ltd. All rights reserved.