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

Some oil refineries will probably struggle to replace imported crude oil if President Trump imposes 25 percent tariffs on products from Canada and Mexico.

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.

As Justin Trudeau warns Canadians they could face "difficult days" ahead, here are four options for retaliation.

Trump also said he was still considering new tariffs on Chinese goods, citing its part in the fentanyl trade. He has threatened a 10% duty on all Chinese goods, after imposing pun