The cause of the rupture and the total volume of oil released after the North Dakota spill remain unclear, officials said.

The nearly 2,700-mile Keystone oil pipeline was shut down Tuesday morning after it ruptured in North Dakota, halting the flow of millions of gallons of crude oil.

The approximately 600,000-bpd Keystone oil pipeline from Canada to the United States remained shut down Wednesday after an oil spill near Fort Ransom, North Dakota, on Tuesday released an estimated 3,