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In an experiment, evapotranspiration (ET) rate of unstressed ’s 8’ greengram or mungbean (Phaseolus radiatus L.) in the and region of Jodhpur during 1996-98 was 2.6 to 4.1 mm/day during early growth, 4.2-5.8 mm/day at peak vegetative stage, 5.0-5.7 mm/day and at flowering or pod formation stage and 1.6-4.4 mm/day at physiological maturity stage. The seasonal ET of greengram was 310 mm with an average yield of 672 kg/ha resulting a water-use efficiency of 2.17 kg/ha/mm. The crop coefficient (ratio of actual to potential ET) was 0.36-0.59 at early growth stage, 0.72 + 1.10 at peak vegetative stage, 0.90-0.97 at flowering or pod formation stages and declined to 0.29-0.71 at the maturity. The crop, if irrigated up to 100% ET rate, the grain yield enhanced from 592 kg/ha to 1 563 kg/ha during the low rainfall year of 1998. The thermal time (growing degree7days) in relation to crop phenology, leaf-tip initiation and branch appearance from mainstream of the crop were also worked out. The day-time energy balance study showed that the excessive water loss from the irrigated crop due to advection was 77% at 30 days after sowing, 133% at 45 days and 58% at 75 days.