The problems of utilizing heavy crude oil and natural bitumens centre on their high viscosity which makes them difficult to produce, store, transport and refine. These factors are reflected in costs. World reserves are substantial, however, perhaps as much as 7 trillion barrels estimated to represent 0.9 trillion barrels of recoverable oil. Data required to determine the cost of finding natural bitumen and heavy oil are roughly the same as for other mineral commodities. Similarly for recovery costs.-from Author
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Prospects for heavy crude oil development ( US, Canada and worldwide).