The North American market prefers exporting diesel and gas produced by its refineries than selling them domestically. That because in the international market the fuels are considered product of “premium” quality which can bring more profit to producers. The higher profitability has an explanation in the biofuels policy implemented in the sector since 2005, called “Clean Air Act”, where refineries need to blend a certain amount of ethanol in gasoline every year.
Everything would be all right if the gasoline hadn’t had a decrease in consumption in the last four years, reaching a 13% fall. And even selling less gasoline, these refineries are still required to purchase a certain amount of ethanol stipulated by the U.S. government, that even when not used, have to be purchased in credits (RIN’s), which would be raising the price of its gallon, which previously cost pennies and now has cost more than one U.S. dollar. So to avoid a much greater loss these refineries would be trying to profit from the sale of gasoline and diesel to other countries.