There will be no material effect on production, Stephen Doolan, a company spokesman based in Calgary, said in an e-mail.
Doolan declined to disclose which unit is undergoing maintenance or the duration of the work.
The plant can process 97,870 barrels of crude oil a day, according to data compiled by Bloomberg. It produces gasoline, jet fuel, diesel, propane, butane and sulfur, according to a company website.
The refinery is adjacent to an upgrader that can process 255,000 barrels a day of oil sands bitumen into lighter crude.
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