Alberta holds the world's fourth-largest proven oil reserves and sends approximately 90% of its crude oil exports to the United States.

From the articleCarney implies US trying to 'break' Canada as Alberta vote loomsAlso in Canada’s Mark Carney makes final appeal against Alberta separation ahead of referendum, Prime Minister Mark Carney says US is trying to break Canada as Alberta votes on separation path, Canada’s PM warns US wants to ‘break us so they can own us’, PM Carney: US Is Trying to Break Canada as Alberta Weighs Separation, Canada at risk? Mark Carney warns as Alberta separation vote nears, Carney says U.S. trying to break Canada as Alberta votes on separation path, Alberta has the world’s fourth-largest oil reserves and sends 90% of its crude exports to the U.S. — It will vote on a first step to leaving Canada | Fortune