Individual caverns within a site can be up to 1,000 m (3,300 ft) below the surface, average dimensions are 60 m (200 ft) wide and 600 m (2,000 ft) deep, and capacity ranges from 6 to 37 million barrels (950,000 to 5,880,000 m3). 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.