| 31. | In the 1970s he worked on the recovery of petroleum from oil shale.
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| 32. | In 1939, the company produced 126, 238 tonnes of oil shale.
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| 33. | Oil shale retorting followed in 1881 by utilization of " D " retorts.
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| 34. | Cheap petroleum prices had driven oil shale out of business.
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| 35. | It was a developer of the Stuart Oil Shale Project.
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| 36. | It is the world's biggest oil shale to energy company.
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| 37. | And the naval petroleum and oil shale reserves would be reduced by 19 percent.
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| 38. | The main business includes coal mining and oil shale processing.
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| 39. | Marble quarries, semiprecious stones, and oil shales were all exploited.
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| 40. | It consists primarily of laminated oil shale, claystone, and siltstone.
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