oasis, an area within a desert where the water table reaches the surface, with enough moisture to permit the growth of vegetation. The water may come up to the surface in springs, or it may collect in mountain hollows. In deserts such as the Sahara, artificial oases have been successfully created by using tube wells, which tap deep sources of groundwater. Oases vary in size, ranging from a pond with a group of date palms to the oasis cities of the deserts of Arabia with extended agricultural cultivation. The ice-free dry valleys of Antarctica are also called oases because they support life surrounded by a barren ice desert.

Fertile tract of land that occurs in a desert wherever a permanent supply of fresh water is available. Oases vary in size from about 2.5 acres (1 hectare) around small springs to vast areas of naturally watered or irrigated land. Underground water sources account for most oases; their springs and wells are supplied from sandstone aquifers whose intake areas may be more than 500 mi (800 km) away. Two-thirds of the population of the Sahara live in oases, where the date palm is the main source of food; the palm also provides shade for growing citrus fruits, figs, peaches, apricots, vegetables, and cereal grains.

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