The crack spread represents the theoretical refining margin. If a crack spread is a positive number then the price of the refined products is higher than that of crude oil, the raw material, and the spread is profitable. If the spread is a negative number,
the products are priced at less than the cost of crude and are not profitable.
The 3-2-1 crack spread is a commonly used formula in the oil industry, expresses the theoretical margin in dollars per barrel.