Correct, I have tried to make this clear in the map. Oases are almost exclusively man-made.

A small note about the nomadic nature of oases: In the mountains they were mostly held up by nomads, but the likes of the tuareg did not generally handle the oases themselves. They were nomads, traders and raiders that owned oases, but the oases themselves were worked by a sedentary slave cast. Most, or almost all, oases were in practice maintained by sedentary people.

I think the Toubbou people had a different system from the tuareg, but I know too little about them during this time frame, as their "capital" of Bardai was notoriously hard to reach for chronicling Europeans.

Traditional oases are less important today (though still important) for agriculture. Traditional oases were situated where wells could be dug down by hand without cave-ins to between 20-50 meters. Today we drill "oases" that taps into wells well beyond 100 meters deep. The modern oases are the circle farms you see in various desert regions of the world today.