Until the end of 2007, the market value of sulphur had remained depressed at $100 a ton, and for one of the longest periods ever. This made the cost of recovery uneconomic so, it was just stockpiled as a result. However, when the price increased five-fold to $500 a ton at the end of 2007, recovery became a profit opportunity for the owners of an oil refinery in Kenai, on the North Slope of Alaska, USA.