We evaluated arbuscular mycorrhizal fungi (AMF) for enhancement of irrigated olive (Olea europaea L.) tree growth and vigour under arid horticultural conditions. The response of 12 common commercial olive cultivars to AMF (Glomus mosseae and Glomus intraradices) inoculation was measured in a nursery experiment. Long-term post-transplanting response to AMF inoculation (G. intraradices alone or G. intraradices + G. mosseae) at the seedling stage was also assessed for 3 cultivars in an irrigated orchard in an arid region. Two control treatments without AMF inoculation were evaluated: one with fertilisers provided as in commercial olive nurseries, the other with no fertiliser application during the time of the inoculation treatments. Inoculated v. uninoculated plants in the nursery showed increases in height, and root and shoot biomass. Intensity of response was highly cultivar-specific. Olive trees inoculated with AMF also performed better than untreated plants in the orchard experiment. Inoculated plants in the nursery showed consistent increases in P and K content both in leaves and roots. Fertilisation at the first growth stage, after rooting, did not contribute to seedling growth and therefore, the practice of stopping fertilisation to promote AMF inoculation was found acceptable. With the correct choice of cultivar–inoculum combination, AMF inoculation technology can benefit olive cultivation, particularly in arid regions where native AMF levels are low.