All else equal, this would increase gasoline prices, which in most of the country have averaged $3 per gallon for the past year amid historically low levels of petroleum inventories (see chart). But Trump wants lower gasoline prices, which is why if the oil tariffs come at all, they will likely start slowly.

Patrick De Haan, head of petroleum analysis at GasBuddy, warned Americans in the Midwest, the Rockies and the Great Lakes regions may be most affected by tariffs on Canada.

Oil futures ticked lower Friday, contributing to a loss for the week, but prices looked to post a gain for the month as traders awaited a tariff decision by President Donald Trump on crude imports from Canada and Mexico.