COMEX copper inventories in the US rose 712% from February 2025 to August 2026, while London and Shanghai stocks fell, Sprott says.
Traders moved metal in to capture higher US prices and ahead of a possible tariff on refined copper. The US now holds about 69% of all exchange-monitored copper.
Supply outside the US has tightened. Available metal on the LME has shrunk to 133,725 tonnes, and Chinese buyers paid the highest import premium in nearly four years last week.
Storage at the Port of New Orleans, the main Comex delivery hub, is largely full.
Commerce has recommended a 15% tariff on refined copper from January 1, 2027, subject to a presidential decision that has yet to come.