Oases can be found in arid or hyper arid areas of all the word appearing in more than 50 countries.
Arid or hyper-arid areas are defined by the named Aridity Index. This index is calculated taking into account the precipitation of the area and the potential evapotranspiration, which is explained by the temperature and the number of hours within a day. Areas in which the Aridity Index is lower than 0.2 can be consider Arid areas, while when the aridity index is lower than 0.05, we can find hyper-arid areas. Arid and hyper arid areas, covers up to 19.6% of global land area.