The productivity and energy balance of sunflower in a semiarid area of Mediterranean climate is studied under three different crop systems, in order to assess the energy efficiency under hydric stress conditions. It is observed that the traditional dryland system, which is scarcely productive in terms of marketable biomass, has a positive energy balance; although this only represents a 9% of the one obtained in the irrigation system, and a 26% of those corresponding to the rational system. The most efficient system in the use of energy is the rational dryland.