An analysis of deficit irrigation in three quite different situations was conducted to better understand the potential benefits and risks associated with this irrigation strategy. Existing crop yield functions and cost functions, developed independently of the present research, were used to estimate the levels of applied water that would produce maximum net income in each situation. These same functions were also used to estimate the degree to which the three crops could be under-irrigated without reducing income below that which would be earned under full irrigation. The analysis encompassed wheat production in the northwestern USA, cotton production in California and maize production in Zimbabwe. Results suggest that (1) deficits of between 15% and 59% would be economically optimal, depending on the circumstances, and (2) the estimated margin for error in these estimates is quite wide.