The dominant question for shale oil production is under what conditions shale oil is economically viable. According to the United States Department of Energy, the capital costs of a "ex-situ" processing complex are $3–10 billion. The various attempts to develop oil shale deposits have succeeded only when the shale-oil production cost in a given region is lower than the price of petroleum or its other substitutes. According to a survey conducted by the RAND Corporation, the cost of producing shale oil at a hypothetical surface retorting complex in the United States (comprising a mine, retorting plant, upgrading plant, supporting utilities, and spent oil shale reclamation), would be in a range of $70–95 per barrel ($440–600/m3), adjusted to 2005 values. Assuming a gradual increase in output after the start of commercial production, the analysis projects a gradual reduction in processing costs to $30–40 per barrel ($190–250/m3) after achieving the milestone of . The United States Department of Energy estimates that the "ex-situ" processing would be economic at sustained average world oil prices above $54 per barrel and "in-situ" processing would be economic at prices above $35 per barrel. These estimates assume a return rate of 15%. Royal Dutch Shell announced in 2006 that its Shell ICP technology would realize a profit when crude oil prices are higher than $30 per barrel ($190/m3), while some technologies at full-scale production assert profitability at oil prices even lower than $20 per barrel ($130/m3).