Tariff Threats Drove Copper Stocks Past 1 Million Tons
As stockpiles hit historic levels, operators should track how shifting arbitrage gaps affect domestic metal costs.
Updated on Oct. 14, 2026 in International Trade
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United States copper stockpiles surpassed 1 million metric tons following a series of tariff threats that began in February 2025. Comex-approved warehouses now hold approximately 70% of global visible copper stocks, significantly altering supply chains leading up to the 15% tariff scheduled for January 1, 2027.
Why it matters
The massive influx of metal was driven by a wide arbitrage gap between the Comex and London Metal Exchange, as traders moved inventory to hedge against incoming import duties. This buildup represents a major shift in commodity availability that impacts procurement costs for businesses reliant on refined copper.
Comex copper stocks have surged nearly 750% since February 2025, reaching a record price of $6.83 per pound on September 22, 2026. While the arbitrage gap between Comex and the London Metal Exchange peaked at over $3,000 per ton in July 2025, it has since narrowed to approximately $310 per ton.
The players
Donald Trump
The current President of the United States who initiated the study on potential copper tariffs.
The details
Traders capitalized on tariff threats by pulling metal from off-exchange markets and funnelling it into Comex-approved facilities to exploit the favorable price differential. This strategy led to significant inventory accumulation in U.S. hubs, including New Orleans and Baltimore, where stocks have risen 44% since mid-August 2026. Operators must monitor how this concentrated inventory levels out as the implementation date for the 15% tariff approaches.
Timeline
February 2025: Trump ordered a study on potential copper tariffs.
July 2025: The arbitrage price gap reached a record peak.
September 22, 2026: Comex copper prices reached record highs.
October 18, 2026: LME Week industry gathering begins in London.
January 1, 2027: Proposed 15% tariff on refined copper imports begins.
Market Landscape
This stockpiling behavior is a direct response to the trade protection measures outlined in the U.S. government's tariff roadmap. It follows the pattern of previous commodity shifts where market participants move inventory ahead of scheduled import duty escalations.
Businesses should review their procurement contracts to determine if they are currently paying premiums based on the narrowed $310-per-ton arbitrage gap. Owners relying on copper should also prepare for potential cost increases as the 15% tariff implementation date on January 1, 2027, draws closer.
The takeaway
The massive buildup of copper inventories demonstrates how tariff-driven arbitrage can temporarily distort local supply levels. Operators should monitor Comex inventory data closely over the next quarter to gauge whether stocks begin to draw down as the 2027 tariff deadline approaches.
What happens next
A 15% tariff on refined copper imports is scheduled to take effect on January 1, 2027, with a further 30% tariff planned for 2028.
Further reading
For broader context on how duties affect supply chain logistics, see International Trade.
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