Daniel Yergin cites an estimate by IHS Cambridge Energy Associates which shows oil from shale and dense rock, which was about 1 million barrels a day in 2011, could reach 3 million barrels a day 2020. North Dakota where much of the production is taking place is now fourth in oil production in the U.S. after Texas, Alaska, and California, and is likely to move up to second place. U.S. imports of oil come primarily from Canada 25%, Mexico 11%, Venezuela 9%, and the Persian Gulf 16%. Canadian oil sands development has increased production and the completion of the Keystone pipeline will increase the share of oil imports from Canada. This is shifting the dynamic of oil away from the Persian Gulf, with the volatile politics in the region, and more towards North America.