The troughs focus sunlight on tubes suspended overhead that contain a synthetic oil.

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The remaining value can be attributed to oil and gas trading and energy products like natural gas, synthetic oil, bitumen and fuel oil.

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Some processes exist that convert coal to synthetic oil.

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Even synthetic lubricating oil is derived from actual petroleum oil.

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By then many refiners will have expanded and upgraded to take not only heavy crude but also synthetic crude from Canada's oil sands.

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"It's not just more people driving, it's also every product that you buy is made of plastic or synthetic materials out of China is made with oil, " said Patrick Chovanec of Tsinghua University.

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For their calculations, the two assumed that where there was a gap between demand and conventional supply it would be filled with synthetic fuels, first with tar-sands oil and later with oil from coal and shale. (According to high-end estimates, coal and oil shale could together yield some ten trillion barrels of unconventional crude.) They then calculated what the impact would be on global carbon-dioxide levels.

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