Ten weighable containers, the same size as 4-gallon petrol tins, were located in a plot 80 metres from the leading edge of a 2-acre field of irrigated alfalfa growing under advective conditions in the Sudan. Evapo-transpiration from alfalfa growing in these containers was compared with evaporation from a series of small evaporimeters level with the top of the plants and from a standard U.S. Class A evaporation pan, and also with estimates of evaporation calculated by the Penman formula. Evaporation from the free water surfaces in evaporimeters or pan was always greater than from alfalfa in the containers when the crop was 25 cm. high or less, but lower when the crop was more than that height, whilst the figures calculated by the Penman formula were much lower than either. Cumulative water losses were also recorded from containers where the soil was kept wet or allowed to dry out, and these were compared with evaporimeter losses up to the stage where no further water was being lost from the dry containers.