Light crudes have low wax content, with lower density and API viscosity.

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Heavy crudes (high wax content, high API viscosity, high density) cannot be refined efficiently by refineries geared to refine light crudes and vice versa.

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Sweet light crude oil yields the most gallons of gasoline per barrel of oil and since it has low viscosity and low density, it is comparatively inexpensive to pump, transport, and refine.

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The majority new oil being developed are heavy, sour crude oils which have a high sulfur content, high viscosity, and high density.

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