User blog comment:Firekirby135/Glass Desert Field Guide/@comment-32362507-20170622180659/@comment-31826059-20170622181917

there are 3 in the area before the area with the giant pillar, 3 in the area with the giant pillar, 1 in the area with the Rock Slime Statues, 2 in the area with the Mosaic Slime Statues, 1 in the area suspended above the flowing sands after the area with the Rock Slime Statues, 1 in the area after the Mosaic Slime Statue, 1 in the Dervish Slime Statue fortress and 1 before the fortress.

So there are 13 oases in total