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Commercial form of oil (could be raw or slightly processed to match the trade specifications).
The most common characteristics used to identify the quality of a crude are its API gravity and its Sulfur content.
Crude is considered sweet if Sulfur content < 0.5 % and sour if Sulfur content > 0.5 %.
Below are the popular examples of market crudes which set up the oil price benchmarks in exchange tradings:
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