US refiners are facing a critical supply crunch from Canada, their largest foreign crude source, as planned maintenance in Alberta is set to cut production by 300,000 barrels a day next month. This comes at a time when US refineries are processing the most crude in eight years, driven by record diesel margins.
The shortfall will hit Midwest refineries hardest, which rely on Canadian oil for 70 percent of their supply. Canada’s oil sands maintenance, scheduled for September, will disrupt the flow of 4 million barrels a day typically sent to the US. Alberta’s stockpiles are already at their lowest in over a year, according to Kpler data, leaving little buffer to absorb the loss.
Enbridge and Trans Mountain pipelines, key export routes, are not rationing space due to maintenance at both ends, signaling reduced shipments. The most recent zero allocation on Enbridge’s Mainline was in October 2025.
Crude prices are already reflecting the tension. Diesel-rich synthetic crude from Canada now trades at a $20-a-barrel premium to US futures, the highest since April’s Iran War spike. This grade, processed from oil sands bitumen, is in high demand as refiners scramble for supply.
Suncor and Canadian Natural Resources plan maintenance at upgraders like Syncrude, further delaying output that was already postponed earlier this year. Last week, US crude imports from Canada dropped sharply, marking the largest decline since May, per Energy Information Administration data.
This decline coincides with heightened Middle East tensions, which have already strained alternative supplies through the Strait of Hormuz. Crude futures hit multi-week highs on Thursday, with gas prices likely to spike ahead of Labor Day travel. Refiners are under pressure to secure alternative sources, but options are limited.
The Canadian shortfall underscores the vulnerability of US supply chains, which have relied heavily on the north during the Iran War. With storage at Hardisty, Alberta, near record lows, the situation could worsen if maintenance extends beyond September.
