Over the last several decades, there has been a sharp decrease in rainfall in the Middle East in general, including Palestine in particular. Indeed, marked increases in the number of droughts, particularly in the southern and eastern slopes of the West-Bank have been noted. Unfortunately, there are projections of a further decline in rainfall in Palestine in the future, which is predicted to be particularly devastating to crop production, including native species. In this study, we sampled leaves of olive trees from 11 different regions of Palestine that vary in water availability. We conducted leaf stable carbon isotope analysis on these trees across their native range in order to better understand the variation in physiological responses that include stomatal conductance and photosynthetic capacity that together determine ci/ca(inter-cellular leaf [CO₂]/atmospheric [CO₂]). The carbon isotope ratios of olive trees showed a range of values that differed by approximately 6 per mil (ranging from -23.6 to -29.2 per mil). However, the correlation between carbon isotope ratios and precipitation did not reflect the expected trend for response to water availability, and may be due to strong adaptations for water-use efficiency, as well as responses of leaves during formation to past years that differ from the collection year. In addition, the oldest tree (possibly greater than 3,000 years old) had carbon isotope ratio values that were different from all of the other younger trees. More specifically, this tree had an isotope value near -29.0% that likely reflects higher stomatal conductance and higher ci/ca values. This study provides a foundation for beginning to determine the degree to which olive responds to water availability and may allow us to choose the most appropriate genetic sources for continued success of olive production in the face of a rapidly changing climate in Palestine.