Evapotranspiration (ET) has been used as an indicator of plant growth and yield. But, the relationship between yield and evapotranspiration is not robust due mainly to the varying contribution of non-productive losses to the total ET. This study was conducted to determine the contribution of interception, soil evaporation, and transpiration to the total ET, and to determine the water use Efficiency (WUE) of two candidate bioenergy crops for the US mid-south region. Swichgrass and high biomass sorghum were grown in a randomized block design at Stillwater, OK. Soil water content measurements were made by neutron probe every two weeks to a depth of 200 cm in 20-cm intervals. From the soil physical properties, deep drainage was estimated using the Darcian method. A Water balance approach was used to calculate ET. ET was partitioned by measuring canopy interception (using interception trays) and soil evaporation (using microlysimeters and modeling). Transpiration was calculated by the difference. WUE was calculated as the ratio of above ground biomass produced to evapotranspiration and transpiration. Result from 2011 and 2012 growing season will be presented in this poster.