The shutdown of TransCanada Corp.’s Keystone and Enbridge’s Platte pipelines in Missouri, due to a possible leak, could squeeze U.S. refiners dependent on heavy crude, an analyst said Feb. 7.

The shutdown cuts off the flow of heavy crude oil from Canada, a major exporter to the U.S. It comes at a time when sanctions against Venezuela have stopped imports from that country, also a major supplier of heavy crude.

Already, the discount of Canadian oil to U.S. benchmark West Texas Intermediate (WTI) has expanded from $9.25 per barrel to $10.30 per barrel in the last day, Greg Haas, director of integrated energy research at Stratas Advisors, told Hart Energy.

“The most recent weekly EIA petroleum data shows Canada exported 3.7 million barrels per day into the U.S., so the combined outage of the affected pipelines adds up to 735,000 barrels per day, or nearly 20% of last week’s imports from Canada,” Haas said. “Potentially, if one or both of these major crude arteries remains out of service for some time, Canadian oil prices will definitely feel the loss of 20% takeaway.”

A portion of the pipelines between Steele City, Neb., and Patoka, Ill., remained shut on Feb 8 as crews excavated a 4,000-square-foot area in the St. Louis area to determine whether a leak occurred.

Haas said this is a particularly bad time because the U.S. just put sanctions into place against Venezuela, a major exporter to the U.S. and another producer of heavy crude in this hemisphere. Last week, EIA data show imports of 345,000 barrels per day (bbl/d) from Venezuela.

Mexico, another major provider of heavy crude to the U.S., shipped an average of 497,000 bbl/d in the week ended Feb. 1. Mexico’s heavy crude premium to the Canadian price expanded nearly $2 in the last 24 hours on signs of shortages of heavy crude in North America, Haas said.

Reuters contributed to this story.

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