For three decades, the Algerian Sahara has experienced strong urban growth, but also a real dynamism of its agriculture, which, both, upset the traditional oasis systems. Nevertheless, the effects of these phenomena differ widely according to the oases considered. The analysis of two traditional oases belonging to the same geographical area, the Ziban, illustrates this diversity of response in terms of spatial organization and agricultural production system. In this context of profound changes, Sidi Khaled, on the northern bank of the oued Djedi, on the sidelines of the center of gravity of Ziban (Biskra), resists agricultural and urban transformations, thanks to its linear organization along the Djedi wadi which preserves it from the process of urban sprawl. Conversely, the oasis of old Tolga is surrounded to the north by the more recent town of Tolga, whose extensions contribute to the sprawl of its territory, while to the south the agricultural development perimeters which adjoin it, exhaust the superficial water table used by the oasis and promote the gradual degradation of the old oasis. The study of these two cases aims to account for the diversity of the mechanisms involved, as well as the factors that sometimes cause the crisis and sometimes favor the maintenance of these oasis ecosystems.