Individual caverns within a site can be up to below the surface, average dimensions are wide and deep, and capacity ranges from . Almost $4 billion was spent on the facilities. The decision to store in caverns was made in order to reduce costs; the Department of Energy claims it is roughly 10 times cheaper to store oil below surface with the added advantages of no leaks and a constant natural churn of the oil due to a temperature gradient in the caverns. The caverns were created by drilling down and then dissolving the salt with water.