U.S. President Donald Trump’s tariffs on Canadian and Mexican imports threaten to disrupt North America’s tightly integrated oil market and push up gasoline prices for American motorists.

Trump on Saturday signed orders implementing a levy of 10% on imports of Canadian energy, along with general levies of 25% on Canada and Mexico and 10% on China, according to White House officials who briefed reporters on condition of anonymity.

Tariffs on Canada and Mexico may curtail shipments from the top two suppliers of foreign crude to the U.S. Almost all of Canada’s roughly 4 million barrels of daily crude exports flow to its southern neighbor, and about 500,000 barrels comes into the U.S. from Mexico, the bulk of it purchased by Valero Energy Corp. for its plants on the Gulf Coast.

In the U.S. Midwest, which is home to 23% of US refining capacity, refiners are so reliant on Canadian supplies that pipelines that once carried oil from the Gulf Coast to the Midwest have been reversed, leaving fuelmakers little access to alternative grades of oil.

“Canadian oil tariffs would risk unpopular, if temporary, gasoline price increases in the US Midwest,” Goldman Sachs Group Inc. analysts including Samantha Dart and Daan Struyven said in a recent note.

Fuelmakers have also warned that the levies will erode refining profits and upend oil markets. US plants could cut refining rates in response, executives at Valero executives said Thursday, while Phillips 66 cautioned that Canadian crude prices will tumble.

The tariffs’ implementation will be key in determining the effect on the market. If producers are allowed to export oil off the Gulf Coast to non-U.S. buyers without tariffs, the hit to Canadian oil prices would be muted. Also unclear is how the tariffs will affect the western Canadian oil that’s shipped through the US en route to Canadian refineries in Ontario and Montreal.

Canada has one partial protection against the tariffs: the newly expanded Trans Mountain pipeline running from Alberta to a marine terminal near Vancouver. The expanded line, which started operation in May, is underused because of its expensive tolls, but it may fill up to maximize tariff-free shipments to Asia at the expense of California refineries, which now import about half the oil from the line.

Mexico’s oil industry, which ships half of its crude exports to the US, also may take a hit. If American fuelmakers including Valero, Chevron Corp. and Phillips 66 turn away from Mexican oil, the alternative would be to boost long-haul sales to Europe and Asia, squeezing margins for state-controlled oil company Petroleos Mexicanos.

Rising fuel costs in the U.S. would indirectly affect Mexico as the country is the top buyer of both diesel and gasoline from the US. That could encourage Mexico to import more from Europe and Asia.

--With assistance from Nathan Risser and Lucia Kassai.

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