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A field experiment with 2,200 m² was performed from 2004 to 2006, in northeast Portugal, to evaluate the response of a commercial olive (Olea europaea L. cv. "Cobrançosa") orchard to different irrigation regimes on growth and yield. The trees were subjected to three irrigation treatments: rainfed conditions (T0), irrigation with 30% (T1) and 100% (T2) of crop evapotranspiration (ET_c). Seasonal dynamics of stomatal conductance (g_s) and shoot water potential varied among treatments, and responded to soil water content and atmospheric evaporative demand. Irrigation increases g_s, in association with increases in water status. Annual ET_c varied from around 300 mm in T0 to 700 mm in T2. Irrigation increased fruit yield, due to the greater number of fruits per tree and higher mass per fruit. Differences in oil yield among treatments were closely related to fruit yield. Moreover, oil accumulation in the fruit was delayed in rainfed conditions. Variations in fruit and oil yield was strongly influenced by variations in ET_c. On average, the amount of oil produced per unit intercepted PAR increased with irrigation and for both irrigated treatments was more than double those of T0. A strategy of continuous deficit irrigation with only 30% of maximum ET_c may have a very beneficial effect, since it allows increasing oil yield to more than double that of rainfed conditions. © 2010 Springer Science+Business Media B.V.