Drilling on the Khorat Plateau of northeastern Thailand and central Laos has outlined what may develop into one of the world's largest potash deposits. The potash is in a salt-bearing sequence of Cretaceous age that underlies about 60,000 km 2 of the plateau. Locally, the deposit is at very shallow depths (90 m), is nearly flat lying, and is as much as 40 m thick. The deposit consists mainly of carnallite, although tachyhydrite and sylvite are also present. High-grade sylvite bodies as much as 34 m thick have been discovered at several localities. The sylvite is apparently the result of leaching of the original carnallite by solutions of unknown origin. In many places the carnallite deposit was completely destroyed, leaving only recrystallized halite. The sylvite bodies seem peripheral to the barren halite, and their size and geometry are not yet known.