Sublimed sulfur (flowers of sulfur), precipitated sulfur, and colloidal sulfur are all excluded from this heading and classified elsewhere. Heading 2503 covers crude and refined bulk sulfur — the forms typically traded as industrial raw material — but not the chemically processed specialty grades used in pharmaceutical or fine-chemical applications.

Canada's large oil-sands upgrading operations and natural-gas processing plants generate substantial quantities of recovered elemental sulfur as a byproduct. Geographic proximity and integrated pipeline and rail infrastructure make Canadian supply the most cost-effective option for US buyers, particularly those in the fertilizer and chemical sectors.