The oases are areas in the middle of the desert where vegetation grows because of the existence of water sources. Those regions that grow the plants are limited and generally small. Sometimes size is not reduced, but still is tiny compared with its extension of the huge sand around them. Oases are fertile, so that they practiced agriculture. Sources of moisture may be from a spring, lake, river, or even groundwater. In some oases cultivated fruit (especially citrus), vegetables and even grains like corn and oats. The oases are centers of population concentration. The two thirds of the population of the Sahara, for example, inhabit them.
The oldest existing oasis is constituted by the banks of the Nile River these, lush vegetation grows in the desert.
In the oases of the Sahara, the date palm is the main source of native food. In addition, crops are grown in its shadow.