The U.S. Secretary of State, Rex Tillerson, has reiterated the potential for sanctions against Venezuelan oil exports, echoing President Trump’s comments from September. Imports of oil from Venezuela are already in decline, having fallen 32% in the fourth quarter on a year earlier. As a result they reached the lowest in a decade in December. Secretary Tillerson wants to mitigate the impact for American business. The largest U.S. importers from Venezuela in the past three years have been Valero (24%), Citgo (21%) and Chevron (11%). Valero and Chevron have plenty of alternative sources,...