The effect of irrigation on the total yield has been observed in a number of research projects (Goldhamer et al.).

The significant contribution of irrigation-to-yield appears to be the increase in the amount of fruit, fruit size and oil content. The yield improvement is probably attributed to increased tree size and leaf area.
It was concluded that for traditional low tree densities, the application of a constant amount of water, 80-120 liters/day/tree (in heavy soils), would provide good results (Pastor et al).

Other research works have indicated an even better response to irrigation (Faci et al). The increase in water application resulted in yields 74% higher   than the driest treatments. This was true for both fresh yield and oil production. The effect on yield accumulation was due both to increasing number of fruits and fruit size. However, Samish & Spigel, 1961 indicated that high oil yields were attributed mainly to an increase in fruit size rather than to the quantity of fruits.

Other works have shown (Tombesi, 1996) that irrigated trees bear more fruit per tree and produce a larger total yield per hectare.
The increase in fruit size is seen in the pericarp and thus increases the flesh/stone ratio.

It can be concluded in general, that high yield is a result of increase both in quantity and fruit size. The differences among the various research projects are probably a result of interaction between irrigation timing and the tree’s phonological status.