President Donald Trump‘s threatened tariffs on Canadian crude oil imports could raise gasoline prices for U.S. drivers if the levies are enacted next month, according to major refiners and energy analysts.

Trump issued an executive order on Feb. 1 imposing a 10% tariff on Canadian energy imports to the U.S., in addition to sweeping 25% levies on goods from from Canada and Mexico. The tariffs are currently on hold until March 4 after Mexico City and Ottawa reached an agreement with the White House.

Refiners particularly in the Midwest have become reliant on Canadian crude imports despite the fact that the U.S. is the largest oil producer in the world, outpacing Saudi Arabia and Russia. This is because Canadian crude is heavier, lower quality and therefore cheaper to purchase, according to Wells Fargo analysts.

Marathon Petroleum processes a significant amount of heavy crude and expects costs to increase if the tariffs on Canadian energy go into effect, CEO Maryann Mannen told investors recently.

“We believe that the majority of that would be borne by the producer and then frankly to a lesser extent the consumer,” Mannen said on the company’s Feb. 4 earnings call. “We’re working with the administration. We’re working with agencies as well as the trade associations to ensure the right people understand the implications of these decisions.”

The U.S. imports nearly 6.6 million barrels per day of crude oil with about 60% coming from Canada, according to Andy Lipow, president of Lipow Oil Associates. Midwest refiners in particular are heavily dependent on these imports with 70% of the crude they process into diesel and gasoline coming from Canada, according to Lipow.

How much fuel prices would rise due to the tariffs depends on how Canadian producers and U.S. refiners respond. In general, a 10% tariff passed to the consumer would increase gasoline and diesel prices by about 15 cents per gallon, Lipow said in a Feb. 2 note.

Canadian prime minister candidate Chrystia Freeland, who previously served as finance minister, has warned that oil producers in Canada have alternatives to the U.S. market.

“There is a danger here for the U.S., and that is Canadians are really angry,” Freeland told CNBC in a Feb. 4 interview. “We will retaliate if we have to. You should be glad that you have us as a reliable energy supplier. We do have alternatives.”

U.S. refiners, however, have “few economically and politically viable alternatives” to Canada’s heavy crude, Mason Mendez, investment strategy analyst at Wells Fargo, told clients in a report Monday. Domestic production could replace some lost Canadian supply but U.S. crude is generally lighter than Canadian oil, Lipow said. Many U.S. refiners have physical limitations on switching totally to light crude oil, he said.

Canadian producers could divert exports from the U.S. East and West Coasts to Europe and Asia instead, Lipow said. This would force U.S. refiners on the East Coast to seek more expensive alternatives in West Africa and West Coast refiners to buy from South America or the Middle East, he said.

In the case of the Midwest, Canada does not have the logistics in place to divert all its exports away from the region, Lipow said. But they would probably try to find other buyers to the extent that they can, he said.

Traders might bid up the price of U.S. crude oil to cover any shortfall in region. Fuel prices might rise by up to 15 cents per gallon as a consequence, Lipow said. But if the tariffs cause local shortages, prices could spike by more than 30 cents per gallon.

The Midwest also does not have easy access to imports through the Gulf Coast because the pipeline system in the U.S. generally runs north to south and west to east, Lipow said.

With few alternatives, U.S. refiners will likely continue to purchase crude from Canada despite the higher cost, Mendez said. They may be able to convince Canadian producers to absorb part of the tariff rather than pass all of it on to the U.S., the analyst said.

“However, even if they split the effects of a 10% tariff, U.S. gasoline prices will likely still rise modestly,” Mendez said.